en/subtitles/3. Swift Programming Language.srt

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[MUSIC]                         

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Stanford University. Okay,      

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well welcome to lecture number  
three of Stanford CS193P,       

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fall of 2017 and                
18 academic year.               

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Today mostly, we're gonna       
talk about some Swift stuff.    

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Now, you've hopefully done      
your homework for the reading,  

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so some of the stuff will       
be kinda summary, but           

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some of this is really not      
covered in the reading.         

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So I'm trying to give you       
the full picture of stuff,      

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that reading is really great    
but it is great concise.        

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I know you probably             
feel like well,                 

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that was a lot of reading for   
something that's concise, but   

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it is quite concise.            
So I'm gonna try and            

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cover some of the other stuff.  
But before I do all that,       

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I'm gonna do a little,          
what I call a teaser demo of    

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auto-layout where I'm gonna     
show you how we can make        

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our UI in concentration look    
good when we rotate the phone,  

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or when we a run on little bit  
different sized iPhone, or      

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whatever. I call it a teaser    
because I don't intend to       

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teach you auto layout which     
is the feature that allows      

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us to do that. It's just to     
show you what's possible.       

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We'll actually have             
a whole lecture on auto         

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layout in about three           
weeks I think. But then,        

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after I do that little demo,    
I'll be back. I'm first gonna   

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take just one minute to         
review what you should have     

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learned by what we did last     
week and I'm literally just     

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gonna read it off a list with   
quick examples. And you can     

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kind of say in your head,       
oh yeah, yeah I got that,       

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I got that or oh wait, I did    
not really understand that and  

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that's a prompt to go back and  
look at it.                     

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Then we'll dive into this long  
list that you see up here,      

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of various Swift things. So     
let's start with this demo I    

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was talking about,              
this auto-layout demo.          

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What we're gonna do here, and   
I apologize for any technical   

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problems we have here because,  
actually, my computer died,     

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and I had to put it. This is    
all brand new computer, so      

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I hope everything's installed   
properly. But here's the code,  

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I think, that we had at         
the end of the last lecture.    

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And the UI looks pretty good.   
We laid it out.                 

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But I just did this by          
dragging these things and       

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using the little dash           
blue lines to put them          

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in position. And when we run    
this thing, it looks okay but   

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only on an iPhone X and         

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only in portrait mode like      
this. If I were to for          

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example, rotate this iPhone     
to the side which I can do      

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in a simulator by going,        
Hardware, rotate left or        

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right, you can see that my UI   
looks like this. My buttons     

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are kind of all jammed in the   
corner here. I've lost flips,   

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it's down here somewhere.       
I can't even see it.            

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Still works, but it's kind of   
off in the middle of nowhere.   

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What we really want is for      
this UI to spread itself        

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out and fill the whole space    
that's involved. By the way,    

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you can also rotate your        
device with Command and         

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the arrows. Kind of a cool      
way to flip back and            

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forth. All right, so            
how are we gonna do that?       

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How are we gonna make our UI    
expand? Let's go ahead and      

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open up here, give              
ourselves some more space.      

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And also I'm gonna              
zoom in a little so             

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you can see. Another thing I'm  
gonna do is we're gonna be      

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using these blue lines,         
the dashed blue                 

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line that appears as you move   
things around as part of this.  

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So I'm gonna change my          
background from black           

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to back to white temporarily,   
just so                         

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that we can see that            
those blue lines and            

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stuff a little bit better.      
So I'm just gonna go to white.  

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When we come to run,            
I'll turn it back to black.     

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So this is purely for dealing   
development issues here. So     

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it's really kinda two things I  
need to do to make this work.   

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One is, I need to kinda         
take all those buttons and      

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make them stick to the edges,   
right?                          

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So that when they rotate and    

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the edges get longer and        
skinnier, they stick.           

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Right now, everything's stuck   
to the upper left corner.       

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The upper left corner, you're   
gonna find out next week,       

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is the origin of drawing. In    
IOS where everything is kinda   

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stuck up to the upper left and  
then just, so                   

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when we rotate it all,          
it just goes off the bottom,    

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we can't see it. So that's      
really what we need to do, but  

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to stick them to the edges,     

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we also kind of need to group   
them together. Because when     

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the edges pull this group       
of 12 buttons apart,            

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they all need to kinda          
share that space.               

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So there's two things           
we have to do.                  

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One is group them together,     
one is pin them to the edges.   

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So we're gonna do that with     
two different features in IOS.  

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One, the grouping               
things together,                

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we're gonna do with stack       
view. Okay, so UI stack view    

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is just another class in IOS    
like UI Button is a class and   

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UI label is just another        
view in fact. And               

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what it does is it will take    
other views, like let's         

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say these four buttons and      
it will stack them together.    

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Now, it only knows how          
to stack horizontally or        

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vertically. It can't stack      
12 of these things in two       

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dimensions like this. So        
I'm gonna have to make three    

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horizontal stacks out of this   
group, out of this group, and   

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out of this group. But then     
I'll take those three stacks    

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and stack them vertically.      
Cuz it's perfectly fine to put  

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stacks inside stacks,           
all right? And once I do that,  

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I'll have all 12 of these       
kinda stocked together. And     

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then I can pin it to the edges  
and they'll stretch out. So     

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how do we make this stack use?  

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Super simple, you just select   
it here. Let me zoom in so      

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we can really see what's going  
on here. We only need the top   

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part for now. So I deselected   
these four things.              

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I'm going down to this          
button right here.              

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You see this button,            
embed and stack?                

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Well, that's what it does.      
It embeds in stack.             

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And it embedded it.             
Now, couple of things.          

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One is, it made the buttons as  
small as it could when you put  

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in the stack. It has 50         
point font, remember, for       

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those emojis. So that's just    
as small as they'll go.         

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It also has no spacing          
between. But I can put spacing  

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in-between by just selecting    
it. It was left selected after  

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I stacked. And going over here  
to the inspector because this   

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stack view, just like           
a button, can be inspected,     

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right? And you can see          
it made it horizontal,          

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it kinda noticed my buttons     
were mostly horizontal. So      

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it picked horizontal. And so    
here's how I set the spacing.   

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I go down here. I'm gonna       
use a standard spacing.         

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There's a lot of places when    
you're doing UI design where    

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you can pick an UI              
standard value and              

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it'll pick a standard spacing.  

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This is a standard              
spacing between buttons.        

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And you wanna use that pretty   
much as much as possible.       

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That way, your UI will be       
spaced like other UI and        

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you will feel like rolling      
on the same page as             

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UI designers across all these   
apps. Also I wanna make sure    

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that these four buttons get     
equal amount of space. Okay,    

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whatever space I am given here  
gets equally distributed and    

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I do that with this             
distribution thing here,        

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I say fill equally. Alignment   
just means I fill the whole     

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space, I could have these       
things being centered or        

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kinda pushed up to              
the top of the stack but        

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I'm gonna have it fill          
the whole space. So that's it.  

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So I'm just gonna do the same   
thing with these two rows.      

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So this one go down here,       
embed in stack,                 

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this group right here           
embed in stack. Oops,           

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I did it twice there. Now I'm   
gonna select both of these.     

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Make them fill equally and      
standard value spacing. So      

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now I've got three horizontal   
stacks. I'm gonna stack these   

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together, I'm gonna             
select them. By the way,        

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dragging to select is really    
an awesome way to select.       

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I highly recommend you do that  
rather than trying to click on  

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things. Because by the way,     
let's say I try to click on     

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here to select this row. Oops,  
I selected the button inside.   

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I didn't want that,             
I wanted the whole row. But     

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if I just drag, not control     
drag but regular drag here,     

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it selects the thing that I     
intercepted with my drag.       

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Anyway, so I'm gonna select     
all three of these with drag.   

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And I'm gonna go embed in       
stack. You put them in          

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a vertical stack. You notice    
this time it's vertical,        

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cuz it noticed those three      
things are vertical.            

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If your things are random,      

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it'll pick the one that it      
thinks is the most likely.      

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You can always change           
it by going here and            

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changing it to the other one.   
So we have vertical,            

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we also wanna fill equally,     
top to bottom here, and         

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we also want standard spacing.  
So                              

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it's great. We got our          
buttons in this nice grid.      

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They're all Perfectly laid      
out in this rectangle. Now,     

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we want to pin this rectangle   
to the edges. Okay, so          

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that when the device rotates,   
or if the device was bigger,    

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like if it was                  
an iPhone 8 Plus, or            

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something like that and         
it was wider, so                

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that it would all just stretch  
out. So, the way we do          

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that is first I'm going to      
use those dash blue lines.      

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I picked up this thing.         
Again, picking it up,           

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you wanna select it first,      
then pick it up.                

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If you don't select it first    
and try to pick it up, oops,    

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you might try and pull one of   
these things out of there.      

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Okay? So, be careful            
about that. All right.          

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So, I'm gonna use               
the blue lines. I'm gonna       

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put this where it               
kinda suggests for              

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the upper left hand corner.     

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You see that? That's pretty     
much where the blue line,       

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that would be the standard      
spacing from the edges.         

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That's what the blue            
lines are telling you.          

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This is a standard              
place to put this. Now,         

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I need to pin it and the way    
we make relationships between   

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views and the UI like pinning   
them to each other and          

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stuff is with control drag.     
Exact same way that we made     

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a relationship between          
our UI and our code,            

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by dragging the code, we do     
the same thing between views.   

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So, I'm gonna control drag      
from this already selected      

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box here to the top. Okay, so   
I'm just dragging up towards    

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the top, and when I let go      
it's going to say, okay,        

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what relationship do you        
want between that view and      

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the top. And there's various    
relationships you can have,     

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like I said, in three           
weeks we're going to have       

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a whole lecture on these        
relationships, but              

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at the very top is the one      
Top Space to Safe Area.         

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You see that Top Space to       
Space Area? The safe area       

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is a safe edge around           
the screen where you can        

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safely draw without             
overlapping some other UI.      

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So, here it's putting it right  
under the place where all       

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the cameras and face            
recognition stuff is all in     

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here. So, it's to keeping it    
below that. Now, if I had       

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other UI on this, like tab      
bars, or title bars, or         

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whatever, then the safety area  
would be inside those. So,      

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we wouldn't overlap our titles  
and stuff. It's really cool.    

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So, I'm gonna put this          
top space little pin, so        

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I'm kinda connected it and you  
can see this blue line appears  

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right here. Okay? This blue     
line here, long blue line.      

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It represents that pinning and  
I can even click on it. Okay,   

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and when I click on it, look,   
it's inspectable in the top     

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half here. Okay? And it's just  
telling me that un-pinned       

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from the safe area top to the   
top of that stack view. And     

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we're zero points               
away from it.                   

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We wanna be right up            
against that safe edge.         

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That's where the blue dashed    
lines told me to put it, so     

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that's where I'm gonna put it.  
Now, we can do the same thing   

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to the left edge over here, so  
I'm gonna control drag over.    

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This time it says,              
Leading Space to Safe Area.     

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00:10:37,069 --> 00:10:40,872
Now, why do you think that      
says leading instead of left?   

215
00:10:40,941 --> 00:10:45,743
Anyone wanna guess? It says     
leading instead of left,        

216
00:10:45,812 --> 00:10:50,081
because some languages Hebrew,  
Arabic, they go right to        

217
00:10:50,150 --> 00:10:53,117
left. The letters come from     
the right, and they flow        

218
00:10:53,186 --> 00:10:55,820
out towards the left. In those  
cases, you want pretty much     

219
00:10:55,889 --> 00:10:58,656
your whole UI flipped over.     
So, you would want these        

220
00:10:58,725 --> 00:11:01,259
buttons pinned to the other     
side, because the text on       

221
00:11:01,328 --> 00:11:03,761
the buttons is gonna be         
coming from the right. Okay?    

222
00:11:03,830 --> 00:11:05,830
Now, it doesn't matter          
with our emojis, but            

223
00:11:05,898 --> 00:11:08,332
that's why we do leading and    
trailing instead of left and    

224
00:11:08,401 --> 00:11:11,435
right. Okay? So, I'm gonna      
click this Leading Space to     

225
00:11:11,504 --> 00:11:14,405
Save Area right here. Connect   
it, I get another little blue   

226
00:11:14,474 --> 00:11:17,141
thing right here. You see       
this one? If I click on it,     

227
00:11:17,210 --> 00:11:19,143
it looks like                   
a little eyebeam,               

228
00:11:19,212 --> 00:11:22,947
it's pinning these 2 and        
it's pinned it with 16 points.  

229
00:11:23,016 --> 00:11:25,950
You see 16 points, evidently    
the blue lines think from       

230
00:11:26,019 --> 00:11:28,986
the left edge, or the leading   
edge you want 16 points.        

231
00:11:29,055 --> 00:11:31,489
Okay, I'll take that.           
And then, of course,            

232
00:11:31,557 --> 00:11:36,026
I could pin to the other side.  
Ctrl+drag over here.            

233
00:11:36,095 --> 00:11:39,397
And now, here I didn't use      
the blue line for that edge.    

234
00:11:39,466 --> 00:11:42,634
So, here if I say trailing      
space to safe area.             

235
00:11:42,702 --> 00:11:44,635
I get an eyebeam,               
this huge, okay.                

236
00:11:44,704 --> 00:11:46,537
So, it goes all the way         
across like that.               

237
00:11:46,606 --> 00:11:50,241
And I don't want that, I want   
it to be the same as the other  

238
00:11:50,310 --> 00:11:53,444
side, 16 points. So,            
in my inspector right here,     

239
00:11:53,513 --> 00:11:56,681
this distance is this constant  
right here, 215 points.         

240
00:11:56,749 --> 00:11:58,882
So, I'm gonna change            
that to be 16,                  

241
00:11:58,951 --> 00:12:02,219
so it matches the other side.   
Oh, and look what happened, it  

242
00:12:02,288 --> 00:12:06,223
pinned the edge of my buttons   
and they spread out, equally,   

243
00:12:06,292 --> 00:12:09,727
filling equally, because we     
told we want to fill equally.   

244
00:12:09,796 --> 00:12:13,664
Okay, so that's pretty cool,    
now we have the bottom.         

245
00:12:13,733 --> 00:12:16,467
So, the bottom is a little      
trickier, because we've got     

246
00:12:16,536 --> 00:12:20,771
flips down here. So, we want    
flips to be on the bottom, and  

247
00:12:20,840 --> 00:12:23,874
we want this thing to           
be above flips. So,             

248
00:12:23,943 --> 00:12:26,310
let's work on flips first,      
let's just get it, so           

249
00:12:26,379 --> 00:12:28,947
that flips is on the bottom     
and we're gonna do exact same   

250
00:12:29,015 --> 00:12:31,549
thing. So, I'm gonna grab       
flips and use the blue lines,   

251
00:12:31,618 --> 00:12:33,517
okay, put it in                 
the center on the bottom.       

252
00:12:33,586 --> 00:12:36,520
And then a controlled           
drag to the bottom,             

253
00:12:36,589 --> 00:12:40,658
and say that I want the bottom  
space to be pinned to the safe  

254
00:12:40,726 --> 00:12:44,962
area. So, that's good.          
Now, when I did that,           

255
00:12:45,031 --> 00:12:47,632
look I got this yellow and      
red lines and                   

256
00:12:47,701 --> 00:12:50,434
I got a warning up here.        
See a warning this warning,     

257
00:12:50,503 --> 00:12:53,037
this means there is a warning   
and it can be red if you have   

258
00:12:53,106 --> 00:12:56,140
an error. And if you click on   
it it will tell you what all    

259
00:12:56,209 --> 00:12:59,210
your warnings are kind of       
a quick summary there, and      

260
00:12:59,278 --> 00:13:02,179
here it says horizontal         
position is ambiguous for       

261
00:13:02,248 --> 00:13:06,183
your flip count label.          
In fact, it is ambiguous.       

262
00:13:06,252 --> 00:13:08,052
I never told it where           
it horizontally,                

263
00:13:08,121 --> 00:13:09,587
I pinned it to the bottom, but  

264
00:13:09,656 --> 00:13:11,322
I didn't say it was in          
the middle, or left, or         

265
00:13:11,390 --> 00:13:14,625
right now I dragged it there    
with a blue lines, but          

266
00:13:14,694 --> 00:13:18,362
starting with blue lines,       
it doesn't pin it there. So     

267
00:13:18,431 --> 00:13:19,897
really what I want              
with flips is,                  

268
00:13:19,966 --> 00:13:22,599
I want it to be in the center.  
Okay, I want it to be in        

269
00:13:22,668 --> 00:13:24,134
center. Just to show you        
something a little different.   

270
00:13:24,203 --> 00:13:27,738
And to do that, again, I        
Control+drag from flips right   

271
00:13:27,807 --> 00:13:30,808
here, to the thing I wanted     
to be in the center of,         

272
00:13:30,876 --> 00:13:33,144
which is this background here.  
So,                             

273
00:13:33,212 --> 00:13:35,112
I'm just gonna Control+drag     
to the background. And          

274
00:13:35,181 --> 00:13:39,750
another option is center this   
horizontally in the safe area.  

275
00:13:39,819 --> 00:13:44,621
So, I'm gonna do that. Now,     
it, it puts it in the middle.   

276
00:13:44,690 --> 00:13:47,758
It's still yellow here.         
So, what does this yellow say?  

277
00:13:47,827 --> 00:13:50,727
It says the frame for the Flip  
Count Label will be different   

278
00:13:50,796 --> 00:13:55,332
at run time. That's, because I  
have not constrained the size   

279
00:13:55,401 --> 00:13:58,168
of this Flip Count Label. I've  
let it be any size it wants.    

280
00:13:58,237 --> 00:13:59,536
And since it can be             
any size it wants,              

281
00:13:59,605 --> 00:14:02,206
it's gonna want to              
be its natural size,            

282
00:14:02,274 --> 00:14:03,841
whatever size fits it.          

283
00:14:03,910 --> 00:14:07,211
Now, I can fix this warning     
down here in this button right  

284
00:14:07,280 --> 00:14:09,813
here. This is where             
all your constraints.           

285
00:14:09,882 --> 00:14:12,984
All this pinning things to      
edges is called constraints     

286
00:14:13,052 --> 00:14:15,686
we're constraining these views  
to be in a certain place,       

287
00:14:15,755 --> 00:14:18,522
that we can just, um, actually  
we don't fix it there,          

288
00:14:18,591 --> 00:14:20,458
but we're gonna fix             
that over here.                 

289
00:14:20,526 --> 00:14:23,627
So, remember, our document      
outline that we had over here   

290
00:14:23,696 --> 00:14:26,464
this little thing we hide.      
If you unhide that and          

291
00:14:26,533 --> 00:14:29,500
look in the upper right, if     
there are any of these little   

292
00:14:29,569 --> 00:14:32,436
warnings you have this little   
button, if you click on it,     

293
00:14:32,505 --> 00:14:34,338
it will tell you all            
the problems. So,               

294
00:14:34,407 --> 00:14:39,310
this one is a misplaced view,   
cuz this flip is too big. For   

295
00:14:39,379 --> 00:14:41,345
what it should be. So, again,   
if you click on this little     

296
00:14:41,414 --> 00:14:44,715
triangle, it'll offer, hey,     
you wanna fix this? And         

297
00:14:44,784 --> 00:14:47,051
you can fix it by updating      
the frames, which we want,      

298
00:14:47,120 --> 00:14:49,653
cuz we don't care what the      
frame this is, the rectangle    

299
00:14:49,722 --> 00:14:51,389
that encloses it. It could      
be anything as long as it's     

300
00:14:51,457 --> 00:14:54,058
pinned to the bottom and        
in the center. And we can       

301
00:14:54,126 --> 00:14:56,160
do other things too, we'll      
talk about a couple of weeks.   

302
00:14:56,229 --> 00:14:58,129
So, I am just gonna update      
frame drive here fix            

303
00:14:58,198 --> 00:15:01,032
missplacement.                  
Look at moved flips down,       

304
00:15:01,100 --> 00:15:04,168
it made the frame around        
it just barely contain it.      

305
00:15:04,237 --> 00:15:07,171
Okay, and now they frame        
around that flip zero is it's   

306
00:15:07,240 --> 00:15:10,407
natural size. If I run this     
and do a hundred flips, so      

307
00:15:10,476 --> 00:15:12,810
that it has to be bigger it     
will naturally get bigger.      

308
00:15:12,879 --> 00:15:15,079
Because it's size               
is not constrained.             

309
00:15:15,147 --> 00:15:17,482
It's not pinned to anything,    
only its location. So,          

310
00:15:17,550 --> 00:15:20,818
its size will get as big, or    
small it needs to to contain    

311
00:15:20,887 --> 00:15:23,521
its stuff. And now, we see we   
have no auto layout issues.     

312
00:15:23,590 --> 00:15:27,591
We have no warning up here,     
all is well. One last thing we  

313
00:15:27,660 --> 00:15:30,661
need to do is the relationship  
between the top of the flips,   

314
00:15:30,730 --> 00:15:34,632
and the bottom of this. Now, I  
could just take this thing up   

315
00:15:34,701 --> 00:15:38,336
here and control drag between   
that and the flips, right?,     

316
00:15:38,405 --> 00:15:40,837
that's a good idea.             
And we could, for example,      

317
00:15:40,906 --> 00:15:43,875
constrain the vertical spacing  
between the two, so I'm gonna   

318
00:15:43,943 --> 00:15:48,679
click Vertical Spacing, there   
it is. It's this huge bar.      

319
00:15:48,748 --> 00:15:52,917
I could go over here and        
change it from 454 to 0, and    

320
00:15:52,985 --> 00:15:55,986
use all the space here. But     
that didn't look very good.     

321
00:15:56,055 --> 00:15:58,722
I don't really like tall        
thin buttons like that.         

322
00:15:58,791 --> 00:16:01,492
So I'm gonna leave this         
constraint in here. But I'm     

323
00:16:01,561 --> 00:16:04,962
gonna change it from equal,     
where it has to be equal,       

324
00:16:05,031 --> 00:16:08,899
to 0 with the flips. Also I     
probably don't want 0, I want   

325
00:16:08,968 --> 00:16:11,936
a standard value here so I'm    
gonna change to standard value  

326
00:16:12,004 --> 00:16:14,605
difference, okay, this,         
this, this distance.            

327
00:16:14,674 --> 00:16:17,007
And I don't it to be equal, I   
want it to be greater than or   

328
00:16:17,076 --> 00:16:19,677
equal. So I just wanna make     
sure that these things on       

329
00:16:19,746 --> 00:16:23,113
the top are always above the    
flips, greater than or equal.   

330
00:16:23,182 --> 00:16:25,716
But it doesn't have to be       
right above it like that. So    

331
00:16:25,785 --> 00:16:28,318
you don't have to always have   
these constraints be equal.     

332
00:16:28,387 --> 00:16:31,388
They can be greater than or     
equal, less than or             

333
00:16:31,457 --> 00:16:35,526
equal kind of relative          
constraints. You see all this?  

334
00:16:35,594 --> 00:16:37,795
Now, we can run the app and     
this should all work.           

335
00:16:37,864 --> 00:16:40,097
Everything is kind of           
constrained to each other.      

336
00:16:40,165 --> 00:16:43,834
We can actually kinda take      
a look at it here in interface  

337
00:16:43,903 --> 00:16:46,470
builder. Right, remember this   
button down here that showed    

338
00:16:46,538 --> 00:16:49,373
us all these phones? We can     
say, okay, what's this thing    

339
00:16:49,442 --> 00:16:52,810
gonna look like on an iPhone    
8? Here's iPhone 8,             

340
00:16:52,879 --> 00:16:55,346
we click on it, and             
sometimes when it does it,      

341
00:16:55,415 --> 00:16:58,015
you can kind of zoom in and     
out to get it to redraw.        

342
00:16:58,084 --> 00:17:00,284
So this is what it's gonna      
look like on iPhone 8.          

343
00:17:00,353 --> 00:17:03,988
We can look at, back on         
iPhone X, but rotate it.        

344
00:17:04,056 --> 00:17:06,557
So here's what it's gonna look  
like rotated on iPhone X,       

345
00:17:06,626 --> 00:17:08,960
that looks like that's          
gonna look okay. So             

346
00:17:09,028 --> 00:17:11,963
we can kind of preview          
a little bit what's going on    

347
00:17:12,031 --> 00:17:13,997
here in interface builder,      
but there's no substitute for   

348
00:17:14,066 --> 00:17:16,667
running it. So let's just       
run it on our simulator and     

349
00:17:16,736 --> 00:17:19,537
see if it looks like            
what we expect.                 

350
00:17:21,040 --> 00:17:23,340
Right here it is,               
app seems to be working. Oh,    

351
00:17:23,409 --> 00:17:27,678
let's go make our background    
black again. So go back here,   

352
00:17:27,746 --> 00:17:32,183
background black, keep our      
Halloween theme intact.         

353
00:17:35,488 --> 00:17:38,655
Right now here, okay, so this   
thing is working we can still   

354
00:17:38,724 --> 00:17:41,458
match things, etc.              
But now when we rotate,         

355
00:17:41,527 --> 00:17:45,496
remember Command+Arrow, look,   
it re-lays out the entire UI    

356
00:17:45,565 --> 00:17:48,766
to fit the space. And           
it's doing this, it's relaying  

357
00:17:48,835 --> 00:17:50,868
it out because of those         
constraints we put it.          

358
00:17:50,936 --> 00:17:53,337
We constrained this edge        
to be stuck to here,            

359
00:17:53,405 --> 00:17:55,573
we constrained this edge        
to be stuck up here.            

360
00:17:55,641 --> 00:17:57,541
We constrained this             
distance to be                  

361
00:17:57,610 --> 00:17:59,610
greater than or                 
equal to a standard distance.   

362
00:17:59,679 --> 00:18:02,980
We constrained the bottom of    
this to be a distance down      

363
00:18:03,049 --> 00:18:05,783
here. We constrained the x      
position of this to be in       

364
00:18:05,852 --> 00:18:08,319
the center. We put those        
constraints on here, and so     

365
00:18:08,388 --> 00:18:12,756
that when we flip this thing    
around, it's living with those  

366
00:18:12,825 --> 00:18:18,095
constraints. Got it? So like    
I said, this is just a teaser   

367
00:18:18,163 --> 00:18:21,031
of this constraint stuff. It's  
a very powerful system for      

368
00:18:21,100 --> 00:18:23,768
doing these constraints and     
we'll talk all about that,      

369
00:18:23,837 --> 00:18:27,738
like I said,                    
in about three weeks. Okay,     

370
00:18:27,806 --> 00:18:30,441
back to the slides.             
All right, so                   

371
00:18:30,510 --> 00:18:32,876
here's your brief               
review of week 1, okay,         

372
00:18:32,945 --> 00:18:35,846
hyperspeed review. Of course    
you know about target action,   

373
00:18:35,914 --> 00:18:38,015
outlet out to out collection,   
outlet collections.             

374
00:18:38,083 --> 00:18:40,651
The card buttons, your flip     
count label. The touch card,    

375
00:18:40,720 --> 00:18:43,454
you know about that. You        
learned all about methods and   

376
00:18:43,523 --> 00:18:46,056
properties, what their syntax   
was for all of those things.    

377
00:18:46,125 --> 00:18:49,794
Properties like flip count and  
tons of methods all the ones    

378
00:18:49,862 --> 00:18:53,397
in concentration in card and    
view controller. You learned    

379
00:18:53,466 --> 00:18:56,367
about property observing right  
when the flip count changed,    

380
00:18:56,435 --> 00:18:58,902
we have that didSet that would  
cause the UI to change as       

381
00:18:58,971 --> 00:19:01,138
well. You obviously             
learned about arrays,           

382
00:19:01,207 --> 00:19:04,041
how to put things in arrays,    
how to declare an array.        

383
00:19:04,110 --> 00:19:06,477
You'll learned a ton about      
model view controller.          

384
00:19:06,545 --> 00:19:09,646
We went and made                
the Concentration game have     

385
00:19:09,715 --> 00:19:12,816
a model like concentration      
on the card.                    

386
00:19:12,885 --> 00:19:15,986
You learned about value types   
versus reference types, right?  

387
00:19:16,055 --> 00:19:18,655
The card, which is a struct,    
a value type that gets copied   

388
00:19:18,724 --> 00:19:21,525
when you throw it around. So    
when we put them in the array   

389
00:19:21,594 --> 00:19:23,961
there, we made the copy by      
just putting it in twice.       

390
00:19:24,029 --> 00:19:25,729
And they copied it each         
time you put it in there,       

391
00:19:25,798 --> 00:19:28,265
remember that? You learned      
about initializers,             

392
00:19:28,334 --> 00:19:31,001
we had initializers both for    

393
00:19:31,069 --> 00:19:32,469
for concentration, they each    
did different things to get     

394
00:19:32,470 --> 00:19:33,870
card and                        

395
00:19:33,940 --> 00:19:36,741
themselves an initializer.      
We didn't initializer for       

396
00:19:36,809 --> 00:19:40,278
our UI view controller and      
we probably never will.         

397
00:19:40,346 --> 00:19:44,548
UI view controllers             
initialization is messy. Okay,  

398
00:19:44,617 --> 00:19:47,585
so we try at all possible       
not to use init for our view    

399
00:19:47,653 --> 00:19:50,154
controller. And I explained     
that in your homework           

400
00:19:50,223 --> 00:19:53,557
that's going out today, you     
can read about it. You learned  

401
00:19:53,625 --> 00:19:56,327
about static methods like get   
unique identifier, static       

402
00:19:56,395 --> 00:19:58,829
vars like the identifier        
factory that we've created      

403
00:19:58,898 --> 00:20:01,698
there. You learned about lazy   
properties like game, which     

404
00:20:01,767 --> 00:20:05,736
depended on another property,   
and so it couldn't initialize.  

405
00:20:05,804 --> 00:20:07,838
We just made it lazy so         
that it wouldn't actually       

406
00:20:07,907 --> 00:20:09,606
initialize until                
someone asked for it,           

407
00:20:09,675 --> 00:20:12,776
which would of course be after  
the thing is all initialized.   

408
00:20:12,845 --> 00:20:15,946
You learned about for           
in loops, which in Swift only   

409
00:20:16,015 --> 00:20:19,183
work by iterating over          
what's called a sequence.       

410
00:20:19,252 --> 00:20:21,852
And we learned that countable   
range is a sequence, right?     

411
00:20:21,921 --> 00:20:24,421
0..< than whatever is           
a countable range,              

412
00:20:24,490 --> 00:20:26,923
that's a sequence.              
But also array is a sequence,   

413
00:20:26,992 --> 00:20:28,893
and string is a sequence        
of characters.                  

414
00:20:28,961 --> 00:20:31,862
A lot of things are sequences,  
you can for in over them.       

415
00:20:31,931 --> 00:20:34,464
We're gonna talk about what     
it means to be a sequence       

416
00:20:34,533 --> 00:20:37,734
little later, probably on       
Wednesday. You learned about    

417
00:20:37,803 --> 00:20:40,637
dictionary. Of course our       
emoji were in a dictionary.     

418
00:20:40,706 --> 00:20:41,839
We learned about                
type conversion.                

419
00:20:41,908 --> 00:20:45,342
We convert types by creating    
a new thing. And using an init  

420
00:20:45,411 --> 00:20:49,480
with the old thing like uint    
32 of an int makes a uint,      

421
00:20:49,548 --> 00:20:53,016
convert into a uint 32. And     
of course, you learned a lot    

422
00:20:53,085 --> 00:20:55,852
about optionals which I'm sure  
are all still new to you and    

423
00:20:55,921 --> 00:20:58,522
I'm gonna talk a lot today      
about optionals and how they    

424
00:20:58,591 --> 00:21:01,058
really work. And what's really  
going on with optionals, okay?  

425
00:21:01,126 --> 00:21:02,759
So that's your                  
review of week one.             

426
00:21:02,828 --> 00:21:04,995
If for some of these, if you    
don't feel like you understand  

427
00:21:05,063 --> 00:21:08,799
these, probably haven't done    
your homework yet, then you     

428
00:21:08,868 --> 00:21:11,402
won't understand this, very     
important. Okay, the first two  

429
00:21:11,470 --> 00:21:13,804
things I'm gonna talk about     
here are just a little quick    

430
00:21:13,873 --> 00:21:17,741
minor things, asides.           
I mentioned doing a for         

431
00:21:17,810 --> 00:21:22,279
loop over floats. So this for   
i = 0.5, i < 15.25 whatever,    

432
00:21:22,348 --> 00:21:26,083
that's something you might      
see in C. You can't do that     

433
00:21:26,151 --> 00:21:28,919
in Swift, okay? Swift doesn't   
have, it only has for in,       

434
00:21:28,988 --> 00:21:32,589
that's all it has. But how do   
we create a countable range or  

435
00:21:32,658 --> 00:21:36,026
some kind of sequence of those  
floats because 0.5...15.25,     

436
00:21:36,094 --> 00:21:40,163
that's actually legal to say,   
but                             

437
00:21:40,232 --> 00:21:44,134
that's only a range in Swift    
not a countable range. And      

438
00:21:44,203 --> 00:21:47,071
that's because we don't know    
what to count by there,         

439
00:21:47,140 --> 00:21:49,739
so it can't create              
a countable range. So           

440
00:21:49,808 --> 00:21:52,977
the way we do that is using a   
global function called stride.  

441
00:21:54,547 --> 00:21:58,114
Stride has form,                
through or from and             

442
00:21:58,183 --> 00:22:00,784
to depending on whether you     
are gonna include the last      

443
00:22:00,852 --> 00:22:04,588
thing, and a by tells you       
what it strides by. Stride is   

444
00:22:04,656 --> 00:22:08,492
function that creates           
a countable range. Countable    

445
00:22:08,561 --> 00:22:11,461
range is a generic type like    
array is a generic type.        

446
00:22:11,530 --> 00:22:13,296
It can count over               
not just ints,                  

447
00:22:13,365 --> 00:22:15,932
it could count over floats, it  
could even count over indexes   

448
00:22:16,001 --> 00:22:18,535
into a string, all kinds of     
things it can count over.       

449
00:22:18,604 --> 00:22:22,172
And this stride knows how to    
create a countable range,       

450
00:22:22,241 --> 00:22:25,476
in this case a closed           
countable range because I did   

451
00:22:25,545 --> 00:22:28,345
through 15.25, not to 15.25.    

452
00:22:28,414 --> 00:22:31,581
It creates one that goes over   
floats and knows to step by     

453
00:22:31,650 --> 00:22:34,951
three, 0.3 there. So that's     
how you do floating point.      

454
00:22:35,020 --> 00:22:37,020
And you don't have to do that   
for your homework or anything,  

455
00:22:37,089 --> 00:22:38,555
but I just wanted to be         
complete about how we do        

456
00:22:38,624 --> 00:22:41,892
a countable range for floats.   
All right, tuples.              

457
00:22:41,961 --> 00:22:45,262
I try to fit everything into    
Concentration that I can,       

458
00:22:45,331 --> 00:22:48,332
an example of everything.       
But I couldn't figure out       

459
00:22:48,400 --> 00:22:51,101
how to fit a tuple in even      
though tuple is a very simple   

460
00:22:51,170 --> 00:22:55,572
little data structure. And all  
that tuple is, essentially,,    

461
00:22:55,641 --> 00:22:59,943
like a mini struct that has no  
methods or vars or anything.    

462
00:23:00,012 --> 00:23:04,114
Just has values in it. So it's  
kind of like struct in other    

463
00:23:04,183 --> 00:23:06,784
languages, like C structs.      
They don't have methods or      

464
00:23:06,852 --> 00:23:08,719
vars or anything, or            
they kind of have vars,         

465
00:23:08,788 --> 00:23:10,554
they have the data stores and   
that's it.                      

466
00:23:10,623 --> 00:23:12,956
So but the tuple is             
super lightweight and           

467
00:23:13,025 --> 00:23:15,392
you kinda define                
everything in line.             

468
00:23:15,461 --> 00:23:19,296
So here's what a tuple looks    
like. Here's a tuple x. x,      

469
00:23:19,365 --> 00:23:23,734
is up here, is of type tuple.   
And this tuple has three        

470
00:23:23,802 --> 00:23:26,437
things in it. A string,         
an int, and a double. And       

471
00:23:26,505 --> 00:23:29,839
I set its value by just         
saying equals parentheses,      

472
00:23:29,908 --> 00:23:33,544
the three things, okay,         
the three values. Now, what's   

473
00:23:33,612 --> 00:23:37,214
kinda cool about a tuple,       
as a lightweight struct kinda   

474
00:23:37,283 --> 00:23:41,451
thing, is that the names of     
the elements is very flexible.  

475
00:23:41,520 --> 00:23:44,855
You can define the names when   
you get the values, like this,  

476
00:23:44,924 --> 00:23:49,092
let parentheses word            
number value equal x. And       

477
00:23:49,161 --> 00:23:52,062
that actually assigns each of   
the values of x to the three    

478
00:23:52,131 --> 00:23:55,833
variables word, number and      
value. Okay? So I'm kind of     

479
00:23:55,901 --> 00:23:59,603
giving these struct elements    
names as I grab them out, or    

480
00:23:59,672 --> 00:24:02,506
we can do the other way         
around. When I define x,        

481
00:24:02,574 --> 00:24:05,042
I can say x is a tuple          
that has a string and           

482
00:24:05,110 --> 00:24:09,045
Internet double called winv.    
Then,                           

483
00:24:09,114 --> 00:24:13,484
when I have x in my hands,      
I can get w,                    

484
00:24:13,552 --> 00:24:16,186
i and v with using,             
using this dot notation,        

485
00:24:16,255 --> 00:24:20,057
kind of like it's a var almost  
in a struct, x.w, x.i, x.v.     

486
00:24:20,125 --> 00:24:23,026
See, so now I'm declaring       
the names when I declare        

487
00:24:23,095 --> 00:24:27,131
the thing. But, and even if     
you do this, you can still      

488
00:24:27,199 --> 00:24:29,766
redeclare the names to be       
something else by saying, let   

489
00:24:29,835 --> 00:24:33,904
word num val = x, it'll crate   
those three local variables so  

490
00:24:33,972 --> 00:24:37,273
super flexible on the naming    
of those three things.          

491
00:24:37,342 --> 00:24:39,943
Usually when we crate a tuple   
we want to use the second way   

492
00:24:40,012 --> 00:24:43,146
the x : i : v way although      
we probably would not use x,    

493
00:24:43,215 --> 00:24:45,615
i and v those are terrible      
names that is just my           

494
00:24:45,684 --> 00:24:47,350
slide only has so much space.   

495
00:24:47,419 --> 00:24:49,386
Horizontally, probably word,    
number or                       

496
00:24:49,455 --> 00:24:51,789
value would have been better    
names. Usually we do that, and  

497
00:24:51,858 --> 00:24:53,457
that's mostly because           
of documentation,               

498
00:24:53,526 --> 00:24:56,226
we want people to know what     
those three things are. If we   

499
00:24:56,295 --> 00:24:59,163
just declare it like x at the   
very top there, string, int,    

500
00:24:59,231 --> 00:25:01,865
double, people are like, hm,    
what are those three things?    

501
00:25:01,933 --> 00:25:03,266
So, what's a tuple good for?    
Well,                           

502
00:25:03,335 --> 00:25:06,336
it's good any time you wanna    
group some stuff together       

503
00:25:06,404 --> 00:25:08,205
that's really lightweight,      
it doesn't have any methods or  

504
00:25:08,274 --> 00:25:10,974
anything associated with it.    
It's also very good for         

505
00:25:11,042 --> 00:25:14,945
returning multiple values from  
a function. A function of       

506
00:25:15,014 --> 00:25:17,781
Swift can only return           
a single thing, but             

507
00:25:17,850 --> 00:25:21,251
that thing could be a tuple,    
and now you can return as many  

508
00:25:21,319 --> 00:25:24,821
things as you want, okay? So    
if I had a function getSize,    

509
00:25:24,890 --> 00:25:28,158
get's a person's size,          
their height and their weight.  

510
00:25:28,227 --> 00:25:32,229
Let's say I can return a tuple  
with weight and height, and     

511
00:25:32,298 --> 00:25:34,898
so when I got it back           
I just x.weight or              

512
00:25:34,966 --> 00:25:38,902
even just getSize.weight or     
getSize.height, access          

513
00:25:38,970 --> 00:25:42,773
it directly. So that's what     
tuples, is I didn't make you    

514
00:25:42,841 --> 00:25:45,109
read about it tuple in your     
first reading assignment but    

515
00:25:45,177 --> 00:25:46,376
you'll be reading about         
it in your next one.            

516
00:25:46,445 --> 00:25:48,178
it's very simple,               
it's exactly what it seems,     

517
00:25:48,247 --> 00:25:50,981
there;s nothing magical here,   
there's no hidden things, it's  

518
00:25:51,049 --> 00:25:56,120
just a simple little struct,    
yeah? Sorry? Do they support    

519
00:25:57,523 --> 00:25:59,589
indexing? Do tuples support     
indexing, you mean like,        

520
00:25:59,658 --> 00:26:04,194
get thing number 1, or get      
thing number 2? Not really,     

521
00:26:04,262 --> 00:26:06,730
and we wouldn't really wanna    
do it that way. If we really    

522
00:26:06,798 --> 00:26:09,299
had something we'd index,       
we'd wanna use an array there,  

523
00:26:09,368 --> 00:26:12,369
because, you know what I'm      
saying? It would obfuscate      

524
00:26:12,438 --> 00:26:14,204
what's going on. The whole      
great thing about tuples,       

525
00:26:14,273 --> 00:26:16,740
you can name each one and let   
people know what they are, so.  

526
00:26:18,477 --> 00:26:21,111
All right, now, okay,           
that was it for                 

527
00:26:21,180 --> 00:26:23,813
little things, now we're back   
to something very important.    

528
00:26:23,882 --> 00:26:27,651
This is a big thing.            
This is computed properties.    

529
00:26:27,720 --> 00:26:30,888
So all the properties that      
you saw in Concentration,       

530
00:26:30,956 --> 00:26:34,057
were stored properties.         
They were just normal vars      

531
00:26:34,126 --> 00:26:36,126
like you're used to in          
another languages, right?       

532
00:26:36,195 --> 00:26:39,429
Like this var foo: Double,      
that's a double precision       

533
00:26:39,498 --> 00:26:42,332
floating point number, and      
it's just stored in memory.     

534
00:26:42,400 --> 00:26:45,536
It's stored with whatever       
struct or class it's part of.   

535
00:26:45,604 --> 00:26:48,405
But it is possible to           
declare foo like this,          

536
00:26:48,474 --> 00:26:53,410
foo Double open curly brace,    
get with the curly brace, set,  

537
00:26:53,478 --> 00:26:55,445
with some curly brace.          

538
00:26:55,514 --> 00:26:59,316
In that case, foo is never      
stored anywhere, instead,       

539
00:26:59,385 --> 00:27:00,751
every time someone asks for     

540
00:27:00,820 --> 00:27:05,255
foo, it gets calculated with    
the code inside get. And        

541
00:27:05,324 --> 00:27:07,624
every time someone              
sets the value of foo,          

542
00:27:07,692 --> 00:27:13,196
this code that's in here        
inside set gets executed.       

543
00:27:13,265 --> 00:27:14,531
Okay, so I got a little         
pointer here. So                

544
00:27:14,600 --> 00:27:17,801
this code gets executed when    
you set, this code up here      

545
00:27:17,870 --> 00:27:21,070
gets executed when you get.     
Instead of it being stored      

546
00:27:21,139 --> 00:27:25,942
somewhere. Now, the set by the  
way, that set(newValue) part,   

547
00:27:26,011 --> 00:27:28,478
that's optional. So you can     
have computed properties        

548
00:27:28,547 --> 00:27:32,215
that are only get, call those   
read only computed properties.  

549
00:27:32,284 --> 00:27:34,618
You can't have ones             
that are only set,              

550
00:27:34,687 --> 00:27:36,920
you can have get only but       
not set only.                   

551
00:27:36,988 --> 00:27:40,523
If you have set only make       
a function set whatever.        

552
00:27:40,592 --> 00:27:44,894
You wouldn't use a var like     
that. Okay, so why a computed   

553
00:27:44,963 --> 00:27:49,065
properties important?           
What do you use them for?       

554
00:27:49,134 --> 00:27:51,835
Well, a lot of times you have   
something that is perceived as  

555
00:27:51,904 --> 00:27:56,940
a property of your struct or    
class that actually is derived  

556
00:27:57,008 --> 00:28:00,510
from other state inside of      
your struct. And when you have  

557
00:28:00,578 --> 00:28:03,313
that situation, you do not      
want to have a stored property  

558
00:28:03,382 --> 00:28:04,881
because you don't               
want to have the same           

559
00:28:04,950 --> 00:28:09,886
information in two different    
vars. Because they can get      

560
00:28:09,955 --> 00:28:11,755
out of sync, all kinds          
of problems happens, so         

561
00:28:11,824 --> 00:28:14,257
you one way or the other        
wants to derive itself          

562
00:28:14,326 --> 00:28:17,761
from the other one. Here's      
an incredibly good example      

563
00:28:17,829 --> 00:28:21,765
indexOfOneAndOnlyFaceUpCard in  
concentration.                  

564
00:28:21,833 --> 00:28:26,736
That is easily derived by       
looking at the cards. So        

565
00:28:26,805 --> 00:28:30,373
you really, we'll really kind   
of bad to have made that        

566
00:28:30,442 --> 00:28:33,143
a stored property, becauase     
we have to keep that thing      

567
00:28:33,211 --> 00:28:37,146
exactly in sync with the face   
up state of all the cards.      

568
00:28:37,215 --> 00:28:41,184
That's really error prone       
way to design. So, we could     

569
00:28:41,253 --> 00:28:44,654
imagine doing, implementing     
indexOfOneAndOnlyFaceUpCard as  

570
00:28:44,723 --> 00:28:45,822
computed property               

571
00:28:45,891 --> 00:28:48,591
with the get just looks at      
all the cards. And if you'll    

572
00:28:48,660 --> 00:28:51,862
only find one FaceUpCard it     
returns that index, otherwise   

573
00:28:51,930 --> 00:28:56,332
it it returns nil. And the set  
just looked to that index,      

574
00:28:56,401 --> 00:28:59,035
make sure that card face up     
and all the rest will face      

575
00:28:59,104 --> 00:29:03,940
down, you see? So, we're just   
using this computed property    

576
00:29:04,009 --> 00:29:07,678
to essentially provide          
this conceptual property,       

577
00:29:07,747 --> 00:29:09,546
which is the                    
indexOfOneAndOnlyFaceUpCard,    

578
00:29:09,615 --> 00:29:11,982
that is the property            
of our game, but                

579
00:29:12,050 --> 00:29:14,885
it's computed from the other    
one. Everyone get what          

580
00:29:14,953 --> 00:29:18,354
I'm saying there? Okay, so      
let's go to Concentration and   

581
00:29:18,423 --> 00:29:20,290
make this change,               
see what this would look like   

582
00:29:20,358 --> 00:29:22,426
if you used a computed          
property here like we           

583
00:29:22,495 --> 00:29:25,228
should've in the first place,   
all right?                      

584
00:29:25,297 --> 00:29:30,700
So let's go back                
here to X code,                 

585
00:29:30,769 --> 00:29:33,971
here we go spring our code      
back up, get rid of that.       

586
00:29:34,039 --> 00:29:38,208
Let's go, oops, let's go to     
concentration, that's where     

587
00:29:38,277 --> 00:29:41,811
this is all right? So everyone  
recognize this code, right?     

588
00:29:41,880 --> 00:29:43,680
This is our entire              
concentration,                  

589
00:29:43,748 --> 00:29:45,882
pretty efficient code as is     
but it's actually gonna look    

590
00:29:45,951 --> 00:29:49,586
even better once we do this     
as you'll see. So we're here,   

591
00:29:49,655 --> 00:29:51,354
we have index and               
one only FaceUpCard. So         

592
00:29:51,423 --> 00:29:54,557
I'm gonna make it computed by   
putting these curly braces in,  

593
00:29:54,626 --> 00:29:57,827
as soon as I do that, now it's  
a computed property. Actually,  

594
00:29:57,896 --> 00:30:00,330
before we do that, let me show  
you even simpler case of this   

595
00:30:00,399 --> 00:30:04,401
just to kinda get you warmed    
up on computed property.        

596
00:30:04,469 --> 00:30:07,804
Sometimes, you have just a      
simple calculation like this.   

597
00:30:07,873 --> 00:30:11,040
The number of pairs of cards    
which are calculated from       

598
00:30:11,109 --> 00:30:14,444
the card buttons, all right?    
There might be other times      

599
00:30:14,513 --> 00:30:17,013
inside our view controller,     
we wanna know this number,      

600
00:30:17,082 --> 00:30:19,949
how many pairs of               
cards do we have. So            

601
00:30:20,018 --> 00:30:23,787
that's kind of a property and   
is derived from this data. So   

602
00:30:23,856 --> 00:30:25,789
I'm gonna take this             
out of here and                 

603
00:30:25,857 --> 00:30:30,127
have number of pairs of         
cards be a property.            

604
00:30:30,195 --> 00:30:35,766
It's gonna be a new var         
numberOfPairsOfCards, and       

605
00:30:35,834 --> 00:30:39,870
it's gonna be of type Int, and  
it's gonna be computed, so      

606
00:30:39,938 --> 00:30:43,339
I'm gonna have a get.           
It's gonna be read only, so     

607
00:30:43,408 --> 00:30:45,976
I'm gonna return this.          
It's not gonna have a set,      

608
00:30:46,044 --> 00:30:49,112
there's no, there's not gonna   
be any set right here. And      

609
00:30:49,181 --> 00:30:52,950
voila I've created a simple     
computed property that's read   

610
00:30:53,018 --> 00:30:56,119
only. By the way if you         
have a read only property,      

611
00:30:56,187 --> 00:31:00,456
you do not actually have to     
have the word get there. So     

612
00:31:00,525 --> 00:31:01,190
a read only property            

613
00:31:01,259 --> 00:31:04,094
can look like that.             
Only if you only have a get,    

614
00:31:04,162 --> 00:31:07,663
if you have a set can't do      
that. So this is a super        

615
00:31:07,732 --> 00:31:10,567
simple little one. So now       
let's go back over here and     

616
00:31:10,635 --> 00:31:12,436
do the little more              
complicated one over here.      

617
00:31:12,504 --> 00:31:16,840
This one does have a get and    
it also has a set. And          

618
00:31:16,909 --> 00:31:20,577
set right here, I put in        
the slide that has newValue.    

619
00:31:20,646 --> 00:31:23,146
This is just gonna be           
the local variable inside here  

620
00:31:23,215 --> 00:31:25,482
that contains the new           
value that someone set,         

621
00:31:25,551 --> 00:31:29,018
indexOfTheOneAndOnlyFaceUpCard  
two. A lot of times we don't    

622
00:31:29,087 --> 00:31:31,421
put anything there,             
if you do that,                 

623
00:31:31,490 --> 00:31:34,858
it defaults to newValue.        
That's the name of the locals,  

624
00:31:34,926 --> 00:31:36,960
there's a special variable      
in here called newValue.        

625
00:31:37,028 --> 00:31:39,562
But if you wanted to call       
it something like index,        

626
00:31:39,631 --> 00:31:42,632
you could do that,              
it's totally up to you,         

627
00:31:42,701 --> 00:31:46,936
a lot of times we just say      
use newValue though. Okay,      

628
00:31:47,005 --> 00:31:50,173
so getting the index            
what do we have to do           

629
00:31:50,241 --> 00:31:53,110
to calculate the index of       
code. So I'm just gonna         

630
00:31:53,178 --> 00:31:56,346
write the little code and have  
a little look of variable,      

631
00:31:56,415 --> 00:32:00,417
say foundIndex which is         
gonna be an optional Int. So    

632
00:32:00,485 --> 00:32:03,453
I'm gonna look through          
all the face cards and          

633
00:32:03,522 --> 00:32:05,622
see if I can find one that's    
gonna be the one I found.       

634
00:32:05,691 --> 00:32:07,490
So I'm gonna use a for          
loop here and                   

635
00:32:07,559 --> 00:32:10,227
go through all the              
cards.indicises, all right?     

636
00:32:10,295 --> 00:32:15,398
I'm gonna look at each card,    
and if that card is FaceUp.     

637
00:32:15,467 --> 00:32:17,667
So I found the FaceUp card,     
whoo-hoo.                       

638
00:32:17,735 --> 00:32:20,870
I'm gonna say, if foundOne      
is nil, in other words,         

639
00:32:20,939 --> 00:32:24,041
I haven't found the card yet    
and this is my first one.       

640
00:32:24,109 --> 00:32:28,211
Then I'm gonna set not          
foundOne, what is it called,    

641
00:32:28,280 --> 00:32:32,849
foundIndex = index, all right?  
So here I'm just saying if I    

642
00:32:32,918 --> 00:32:35,985
just found my first             
one let's remember it.          

643
00:32:36,054 --> 00:32:39,522
Otherwise, if foundIndex is     
not nil that means this is      

644
00:32:39,591 --> 00:32:41,958
the second FaceUpCard           
that I found.                   

645
00:32:42,027 --> 00:32:44,494
Cuz I already found one and     
I found another one, so         

646
00:32:44,563 --> 00:32:47,431
here I am just gonna to return  
nil. Because if there's two     

647
00:32:47,499 --> 00:32:49,900
FaceUpCards then obviously      
the index of the one and        

648
00:32:49,968 --> 00:32:53,270
only FaceUpCard is nil,         
there's no such thing. And      

649
00:32:53,339 --> 00:32:55,371
if I make it all the way        
through this for                

650
00:32:55,440 --> 00:32:58,708
loop I'm just gonna return the  
foundIndex, which is either     

651
00:32:58,776 --> 00:33:01,211
going to have been set to       
the one card I found or         

652
00:33:01,280 --> 00:33:03,680
it'll still be nil              
from this declaration.          

653
00:33:03,748 --> 00:33:05,682
Remember that                   
optionals always get            

654
00:33:05,750 --> 00:33:09,051
this free equals nil when       
they're declared, right? So it  

655
00:33:09,120 --> 00:33:12,222
starts out nil and if I never   
found one, it'll still be nil,  

656
00:33:12,291 --> 00:33:15,692
which is right cuz that means   
there'll be no FaceUpCards.     

657
00:33:15,761 --> 00:33:18,395
We're gonna understand this     
simple code right here,         

658
00:33:18,464 --> 00:33:20,730
how about the set case?         
On the set case,                

659
00:33:20,799 --> 00:33:22,198
I'm just gonna loop             
through all the cards and       

660
00:33:22,267 --> 00:33:26,236
turn all face down except for   
this one that they just set it  

661
00:33:26,304 --> 00:33:29,338
to, which is gonna be new       
value, all right? So I'm just   

662
00:33:29,407 --> 00:33:33,243
gonna go through my cards for   
index in cards.indices.         

663
00:33:33,312 --> 00:33:36,412
Great way to go iterate         
through this countable          

664
00:33:36,481 --> 00:33:39,348
range of all the indexes        
in my array. I'm gonna say,     

665
00:33:39,417 --> 00:33:45,756
cards.index.isFaceUp = false,   

666
00:33:45,824 --> 00:33:50,327
for most cards.                 
But in case the index here,     

667
00:33:50,395 --> 00:33:54,264
this index equals the new       
value of this, then I'm gonna   

668
00:33:54,332 --> 00:33:59,369
set it to true. Okay, so        
here this is an expression      

669
00:33:59,438 --> 00:34:03,874
that's true if someone said     
indexOfTheOneAndOnlyFaceUpCard  

670
00:34:03,942 --> 00:34:07,210
equals whatever. If this        
is the whatever they said,      

671
00:34:07,279 --> 00:34:10,547
then we're gonna have this be   
true if the card's face up,     

672
00:34:10,615 --> 00:34:13,549
o therwise this will always     
be false. Everybody got this    

673
00:34:13,618 --> 00:34:17,553
little code right there? Come   
through with that? All right,   

674
00:34:17,622 --> 00:34:21,391
that's it. Okay, now the        
indexOfTheOneAndOnlyFaceUpCard  

675
00:34:21,459 --> 00:34:22,859
is computed like this,          

676
00:34:22,927 --> 00:34:26,329
from the card, we do not need   
to take responsibility for      

677
00:34:26,398 --> 00:34:30,233
doing things like setting it    
to nil here. This is the case   

678
00:34:30,302 --> 00:34:33,136
where we found two cards,       
we got two cards that we're     

679
00:34:33,204 --> 00:34:36,273
trying to match, well,          
obviously there's two cards.    

680
00:34:36,341 --> 00:34:38,474
So we had to set the            
indexOfTheOneAndOnlyFaceUpCard  

681
00:34:38,543 --> 00:34:40,744
to nil cuz there were two.      
But we don't have to do that    

682
00:34:40,812 --> 00:34:42,912
anymore, because it's           
always computing that,          

683
00:34:42,981 --> 00:34:45,749
every time we ask, it goes and  
looks at the card. And          

684
00:34:45,817 --> 00:34:49,418
even better than that is        
this case down here. Okay,      

685
00:34:49,487 --> 00:34:51,520
this case down here,            
we are setting the              

686
00:34:51,589 --> 00:34:53,523
indexOfTheOneAndOnlyFaceupCard  
to                              

687
00:34:53,592 --> 00:34:56,259
be the index. That's because    
this was the case where there   

688
00:34:56,328 --> 00:34:57,894
were already two or             
there were none,                

689
00:34:57,963 --> 00:35:01,364
and now we turn those           
faceDown and do this new one.   

690
00:35:01,433 --> 00:35:04,734
So we're already setting this   
and it does all of this.        

691
00:35:04,802 --> 00:35:07,470
Setting this thing to           
something already turns all     

692
00:35:07,539 --> 00:35:11,641
the other cards faceDown. And   
already sets that card faceUp,  

693
00:35:11,709 --> 00:35:16,178
so we don't need any of that    
code. So you see how making     

694
00:35:16,247 --> 00:35:20,083
the computed property makes     
this code much simpler and      

695
00:35:20,152 --> 00:35:23,819
straightforward. Cuz it really  
gets at the heart of what's     

696
00:35:23,888 --> 00:35:26,656
going on. I'm just setting the  
indexOfTheOneAndOnlyFaceUpCard  

697
00:35:26,725 --> 00:35:27,223
to this index                   

698
00:35:27,292 --> 00:35:28,191
that I just clicked on or       

699
00:35:28,260 --> 00:35:30,727
I'm just turning this card      
faceUp. And the next time       

700
00:35:30,795 --> 00:35:34,063
someone asks for the            
indexOfTheOneAndOnlyFaceUpCard  

701
00:35:34,132 --> 00:35:36,466
it's gonna do the right thing,  
right?                          

702
00:35:36,535 --> 00:35:39,302
So let's go and run,            
make sure we didn't break       

703
00:35:39,371 --> 00:35:43,306
anything making this into a     
computed property. Here we go,  

704
00:35:43,374 --> 00:35:46,009
hopefully we can still match,   
yeap, that matches,             

705
00:35:46,077 --> 00:35:48,645
and the matching is working,    
and the mismatching is also     

706
00:35:48,714 --> 00:35:52,982
working. Really cool            
computed properties,            

707
00:35:53,050 --> 00:35:55,718
you're gonna see computed       
properties everywhere in iOS,   

708
00:35:55,787 --> 00:36:01,223
they get very common, yeah.     
>> [INAUDIBLE]                  

709
00:36:01,292 --> 00:36:02,258
>> Okay great question, so      

710
00:36:02,326 --> 00:36:04,995
when would I reuse              
this var versus                 

711
00:36:05,063 --> 00:36:07,664
having two methods,             
one which get's the index and   

712
00:36:07,732 --> 00:36:09,833
one really [INAUDIBLE] and      
one that sets it.               

713
00:36:09,901 --> 00:36:14,003
Okay, it's all about whether    
it's perceived as property.     

714
00:36:14,072 --> 00:36:17,807
This index in effect is         
perceived by us as programmers  

715
00:36:17,875 --> 00:36:20,710
it's a property right? It's,    
it's a property of the game     

716
00:36:20,779 --> 00:36:22,379
is the index on the face        
of the card, so                 

717
00:36:22,447 --> 00:36:27,049
that's what you would do here.  
If another way of kind of       

718
00:36:27,118 --> 00:36:32,021
deciding is if the set or the   
get really does a lot of work.  

719
00:36:32,090 --> 00:36:35,158
Like it's really                
crunching on something,         

720
00:36:35,227 --> 00:36:36,826
you might wanna make            
that a function.                

721
00:36:36,895 --> 00:36:38,628
Just so the people don't        
think, oh it's a lightweight    

722
00:36:38,696 --> 00:36:41,731
little property that I can      
get. Now, this might seem like  

723
00:36:41,800 --> 00:36:43,966
a lot of work but it's          
actually very very simple.      

724
00:36:44,035 --> 00:36:46,703
And then later in the lecture,  
probably on Wednesday,          

725
00:36:46,771 --> 00:36:50,073
I'm gonna show you an even      
much simpler version of this.   

726
00:36:50,141 --> 00:36:51,775
When we learn a little          
bit more about Swift.           

727
00:36:51,843 --> 00:36:53,676
But it really is not that much  
work it's just looking at       

728
00:36:53,745 --> 00:36:56,412
another data structure. But if  
you were doing a lot of work    

729
00:36:56,481 --> 00:36:58,114
then you probably               
want to do set and              

730
00:36:58,182 --> 00:37:01,651
get to make it clear.           
But otherwise if it is          

731
00:37:01,720 --> 00:37:06,322
a var if it seems like a var    
make it a var. Good question.   

732
00:37:06,391 --> 00:37:09,892
Alright where is my,            
here it is, keynote,            

733
00:37:09,961 --> 00:37:13,897
lets go back here,              
back to our slides. All right,  

734
00:37:13,965 --> 00:37:17,199
so the next thing we're         
gonna talk about is here,       

735
00:37:17,268 --> 00:37:20,303
is another topic something we   
knew, access control. Okay, so  

736
00:37:20,372 --> 00:37:23,372
what is access control? So,     
how many people have worked on  

737
00:37:23,441 --> 00:37:27,243
a project, an object oriented   
program project of more         

738
00:37:27,312 --> 00:37:31,147
than a dozen classes?           
Okay, like two or               

739
00:37:31,216 --> 00:37:35,284
three of you, four maybe, so,   
not very many of you. Okay,     

740
00:37:35,353 --> 00:37:37,853
well when you're working on a   
very small project like that,   

741
00:37:37,922 --> 00:37:40,056
you can call any method         
in any class, whatever,         

742
00:37:40,124 --> 00:37:42,224
you're probably the only        
programmer working on it.       

743
00:37:42,293 --> 00:37:44,627
Or maybe you're working         
out with a buddy, and so        

744
00:37:44,695 --> 00:37:47,229
you can talk to each other.     
Okay, but now imagine           

745
00:37:47,298 --> 00:37:50,967
that you're working for         
Google. Or Facebook, or Apple,  

746
00:37:51,035 --> 00:37:54,471
or something like that, and     
this is kind of ridiculous.     

747
00:37:54,539 --> 00:37:57,273
But let's say you're working    
on concentration there. And     

748
00:37:57,342 --> 00:37:59,942
there's a whole another group   
in another building that does   

749
00:38:00,011 --> 00:38:03,546
game design and                 
they write the model. And       

750
00:38:03,615 --> 00:38:05,848
you are just the UI team for    
IOS,                            

751
00:38:05,917 --> 00:38:08,050
until you're only writing       
the view controller.            

752
00:38:08,119 --> 00:38:11,054
Okay, well now, you don't       
wanna be calling each others    

753
00:38:11,122 --> 00:38:13,656
code just willy-nilly.          
Calling any old method like     

754
00:38:13,724 --> 00:38:16,225
you wouldn't want your view     
controller cal someone like     

755
00:38:16,294 --> 00:38:17,761
indexOfOneAndOnlyFaceUpCard.    

756
00:38:17,829 --> 00:38:20,363
If those guys are like they     
got rid of that method          

757
00:38:20,431 --> 00:38:23,566
into the next month, and        
now your code broke. Now,       

758
00:38:23,634 --> 00:38:26,236
there are some methods that     
you have to be able to call     

759
00:38:26,304 --> 00:38:29,172
over there and their code,      
and we're gonna make it clear   

760
00:38:29,241 --> 00:38:31,541
which ones of those             
are using access control.       

761
00:38:31,610 --> 00:38:35,244
So access control about having  
keyword that we're gonna put    

762
00:38:35,313 --> 00:38:37,981
into our API, put it on         
the methods and bars,           

763
00:38:38,049 --> 00:38:41,684
it says to other groups that    
we're programming with, yes,    

764
00:38:41,753 --> 00:38:45,088
you are allowed to call this,   
I promise not to break this     

765
00:38:45,156 --> 00:38:48,892
on you. It also tells them      
how to use your thing because   

766
00:38:48,960 --> 00:38:51,794
the ones they're allowed to     
call or the ones they should    

767
00:38:51,863 --> 00:38:54,997
be using to use your            
concentration game or           

768
00:38:55,066 --> 00:38:57,300
whatever. So                    
what are these keywords?        

769
00:38:57,368 --> 00:39:01,237
Well the first one is called    
internal. These are keywords    

770
00:39:01,306 --> 00:39:04,541
you put in front of vars and    
funcs. Or even classes and      

771
00:39:04,609 --> 00:39:07,176
structs, you can make           
entire classes and structs,     

772
00:39:07,245 --> 00:39:10,813
have their access controlled.   
So the default internal,        

773
00:39:10,881 --> 00:39:12,682
this one we never               
actually type in                

774
00:39:12,751 --> 00:39:15,485
because it's the default.       
So all of the methods and       

775
00:39:15,554 --> 00:39:17,653
vars that we've done so         
far in Concentration are all    

776
00:39:17,722 --> 00:39:20,656
internal. Now what does         
internal Access Control mean?   

777
00:39:20,725 --> 00:39:26,061
It means anyone in your app,    
any object, any code anywhere   

778
00:39:26,130 --> 00:39:29,665
can call that method or access  
that bar. So it's pretty much   

779
00:39:29,734 --> 00:39:33,335
unlimited control inside your   
app. Now as we start talking    

780
00:39:33,404 --> 00:39:35,772
about access control, we have   
to realise there's always two   

781
00:39:35,841 --> 00:39:39,442
kinds of programming,           
there's writing an app,         

782
00:39:39,510 --> 00:39:42,445
then there's writing            
a framework. Like Apple does,   

783
00:39:42,514 --> 00:39:46,582
UI kit, okay? That's            
framework. A lot more access    

784
00:39:46,651 --> 00:39:49,285
control issues if you're        
writing a framework. So         

785
00:39:49,354 --> 00:39:51,120
I'm gonna tell you              
what the things are for         

786
00:39:51,188 --> 00:39:53,789
writing a framework but, We're  
not gonna really pay much       

787
00:39:53,858 --> 00:39:55,625
attention to them because we    
are only going to learn to      

788
00:39:55,694 --> 00:39:59,228
write apps in this course. So   
internal means everything in    

789
00:39:59,296 --> 00:40:02,699
your app, or in your framework  
is, can access this code.       

790
00:40:02,767 --> 00:40:05,000
So it's pretty much             
almost unlimited inside         

791
00:40:05,069 --> 00:40:08,671
your Apple framework. Then      
there's the three privates.     

792
00:40:08,740 --> 00:40:10,473
These are very important,       
these are the ones you're       

793
00:40:10,542 --> 00:40:14,143
gonna be using all the time.    
One is just private,            

794
00:40:14,212 --> 00:40:17,313
that means its internal         
implementation to this object,  

795
00:40:17,381 --> 00:40:22,384
no other objects can call it.   
This is a good one to set,      

796
00:40:22,453 --> 00:40:25,722
it keeps someone in the other   
group at Google and the other   

797
00:40:25,790 --> 00:40:28,858
building from accessing         
that code. Because you're       

798
00:40:28,927 --> 00:40:31,527
keeping it private, it's        
your private implementation.    

799
00:40:31,596 --> 00:40:35,164
Private set is almost exactly   
the same, it's only for vars,   

800
00:40:35,232 --> 00:40:39,201
it means that setting this var  
is private, but getting it      

801
00:40:39,270 --> 00:40:43,639
is not private. So you allow    
people to get the var, access   

802
00:40:43,708 --> 00:40:46,676
it, but they can not set it.    
That's you point of view,       

803
00:40:46,744 --> 00:40:48,611
that's your internal            
implementation sets it.         

804
00:40:48,679 --> 00:40:51,514
We'll see a good example        
of that in concentration.       

805
00:40:51,583 --> 00:40:54,850
And then there's fileprivate.   
Fileprivate in a Swift file,    

806
00:40:54,919 --> 00:40:56,852
you can have multiple           
classes and structs in there,   

807
00:40:56,921 --> 00:40:58,955
you don't have to be just one   
class which is what we've done  

808
00:40:59,024 --> 00:41:02,158
so far and fileprivate means    
anything in that in that        

809
00:41:02,227 --> 00:41:06,162
file can access each other,     
right. So classes,              

810
00:41:06,230 --> 00:41:09,665
four classes in there, it can   
each others methods, okay,      

811
00:41:09,734 --> 00:41:12,501
that's what file private        
means. Okay, the other ones     

812
00:41:12,570 --> 00:41:15,204
are public and open, those      
are for framework writers.      

813
00:41:15,273 --> 00:41:18,007
Public means that people        
outside the framework           

814
00:41:18,076 --> 00:41:21,444
can call it. Doesn't make       
sense for outside your app,     

815
00:41:21,512 --> 00:41:23,746
that would never happen,        
so outside your framework.      

816
00:41:23,815 --> 00:41:26,416
And open means not only can     
people outside your framework   

817
00:41:26,484 --> 00:41:29,585
call it but they could          
sub class that class,           

818
00:41:29,654 --> 00:41:31,320
override your methods           
all that stuff,                 

819
00:41:31,388 --> 00:41:35,124
so open is like wide open,      
okay. We don't care about that  

820
00:41:35,193 --> 00:41:38,361
cuz we're only, we're not       
doing frameworks, right. So     

821
00:41:38,430 --> 00:41:41,030
we're gonna focus on private    
of the various privates.        

822
00:41:41,099 --> 00:41:43,999
A good strategy to use these    
is pretty much put private on   

823
00:41:44,068 --> 00:41:46,969
anything until you're sure,     
yeah I want someone else to be  

824
00:41:47,038 --> 00:41:48,904
able to call this               
method somewhere.               

825
00:41:48,973 --> 00:41:53,509
Right that's by default you     
should make things private. So  

826
00:41:53,578 --> 00:41:56,312
let's look a concentration,     
what it would look like to      

827
00:41:56,381 --> 00:41:58,114
put access control and          
concentration and               

828
00:41:58,182 --> 00:42:00,883
pay attention here because      
I'm gonna require in all your   

829
00:42:00,952 --> 00:42:04,153
homeworks going forward that    
you mark things properly.       

830
00:42:04,222 --> 00:42:05,922
I want you to mark things       
private if they should be       

831
00:42:05,990 --> 00:42:08,224
private. Okay, cuz I wanna      
just make sure that you         

832
00:42:08,292 --> 00:42:11,895
understand what this is all     
about. So let's go back here    

833
00:42:13,565 --> 00:42:16,665
to Xcode. Let's start           
with our ViewController.        

834
00:42:16,734 --> 00:42:19,134
Okay, we have three classes,    
or three data structures,       

835
00:42:19,203 --> 00:42:21,304
our ViewController, Card, and   
Concentration. So let's start   

836
00:42:21,372 --> 00:42:27,210
with ViewController. So this    
right here is our model. So     

837
00:42:27,278 --> 00:42:31,514
would we want our model to be   
public, to be not private?      

838
00:42:31,583 --> 00:42:33,582
Well that depends, actually.    

839
00:42:33,651 --> 00:42:36,319
It depends of what your model   
is and how it works. Often,     

840
00:42:36,387 --> 00:42:40,256
ViewControllers models          
are public by public I mean     

841
00:42:40,325 --> 00:42:43,492
non-private. We're inside an    
app so forget about public and  

842
00:42:43,561 --> 00:42:47,096
open keywords. I mean, when I   
say public I mean non-private.  

843
00:42:47,165 --> 00:42:49,932
So a lot of times you do        
because you give a model to     

844
00:42:50,001 --> 00:42:51,433
a view controller and           
it displays it,                 

845
00:42:51,502 --> 00:42:54,870
that's what it does. But that   
is not the case here. This one  

846
00:42:54,939 --> 00:42:58,240
wants to be private. And the    
reason it wants to be private   

847
00:42:58,309 --> 00:43:01,477
is because the number of        
pairs of cards in the game is   

848
00:43:01,545 --> 00:43:04,480
intimately tied to the UI,      
okay the number of              

849
00:43:04,549 --> 00:43:07,083
cards we have in the UI.        
So if we wanted to make         

850
00:43:07,151 --> 00:43:09,585
this public then we'd also      
have to make something public   

851
00:43:09,653 --> 00:43:13,356
to specify the number of card   
buttons that we allow and       

852
00:43:13,425 --> 00:43:15,391
we don't do that currently,     

853
00:43:15,460 --> 00:43:18,127
that's something that is        
in our little scene and         

854
00:43:18,195 --> 00:43:21,430
interface builder, so we don't  
do it. So we keep this, we      

855
00:43:21,499 --> 00:43:25,067
keep this private. How about    
number of pairs of cards?       

856
00:43:25,136 --> 00:43:28,271
Well, this is one where I       
don't mind if someone asks      

857
00:43:28,340 --> 00:43:30,706
what the number of              
pairs of cards is but           

858
00:43:30,775 --> 00:43:36,612
setting the number of pairs     
of cards would be bad. But      

859
00:43:36,680 --> 00:43:40,816
the thing about this is it's    
already a get-only property.    

860
00:43:40,885 --> 00:43:43,419
You can't set it anyway,        
it derives it from other data.  

861
00:43:43,488 --> 00:43:47,022
So we're just gonna make this   
private, sorry, not private.    

862
00:43:47,091 --> 00:43:49,358
And we're gonna allow           
people to call this,            

863
00:43:49,427 --> 00:43:51,493
people who are using my         
ViewController, they can say,   

864
00:43:51,562 --> 00:43:53,496
how many pairs of cards are     
there? But they can't set it,   

865
00:43:53,565 --> 00:43:55,998
cuz this is not settable        
anyway. Okay, so                

866
00:43:56,067 --> 00:43:57,366
that's okay to make             
that in public.                 

867
00:43:57,435 --> 00:43:59,902
Same thing flipCount,           
I think flipCount,              

868
00:43:59,970 --> 00:44:03,272
it's okay for people to get     
it, but definitely, we don't    

869
00:44:03,341 --> 00:44:06,508
want people setting flipCount.  
That's something we do          

870
00:44:06,577 --> 00:44:08,978
internally when the cards are   
flip, we implement flipCount.   

871
00:44:09,046 --> 00:44:12,148
So that's private for the       
setter, but will allow people   

872
00:44:12,216 --> 00:44:14,684
to get the flipCount who        
are using our thing.            

873
00:44:14,752 --> 00:44:19,021
Our outlets, almost always      
we have private outlets.        

874
00:44:19,090 --> 00:44:19,989
Cuz our private outlets,        

875
00:44:20,057 --> 00:44:23,159
these things, and even our      
actions these are all kind of   

876
00:44:23,227 --> 00:44:26,295
internal implementation of      
how we implement our UI.        

877
00:44:26,364 --> 00:44:29,365
That's what a ViewController    
does it controls our UI.        

878
00:44:29,433 --> 00:44:32,702
Definitely something like       
update model from UI would be   

879
00:44:32,771 --> 00:44:35,271
private, that's internal        
implementation.                 

880
00:44:35,339 --> 00:44:38,808
All this emoji business that's  
all private. Although you       

881
00:44:38,876 --> 00:44:42,845
could imagine trying to expose  
some public API eventually      

882
00:44:42,914 --> 00:44:45,848
in this ViewController that     
let's someone who's using       

883
00:44:45,917 --> 00:44:49,051
our ViewController specify      
the emojis they want.           

884
00:44:49,120 --> 00:44:53,756
Like, you know, this theme      
required task that you have,    

885
00:44:53,824 --> 00:44:57,460
you could imagine that there    
was a way to specify I want     

886
00:44:57,528 --> 00:44:59,995
you mister view controller      
to play this game,              

887
00:45:00,064 --> 00:45:02,998
but I want you to use           
this emoji as your theme.       

888
00:45:03,067 --> 00:45:05,534
See, so you could imagine       
that something being public.    

889
00:45:05,603 --> 00:45:08,471
I don't think it would          
be exactly this API,            

890
00:45:08,539 --> 00:45:10,439
it would be some                
other kind of API,              

891
00:45:10,508 --> 00:45:13,942
I'm not sure what they would    
let you set the emoji to        

892
00:45:14,011 --> 00:45:16,946
use. We can't really make this  
public cuz we actually consume  

893
00:45:17,014 --> 00:45:20,883
this. This is a var and we      
consume it. We have obviously   

894
00:45:20,952 --> 00:45:23,119
had to deal with that in        
your homework I'm sure. And     

895
00:45:23,187 --> 00:45:24,954
you know, this dictionary       
we're building on a fly,        

896
00:45:25,022 --> 00:45:26,755
we wouldn't want anyone         
messing with it, so             

897
00:45:26,824 --> 00:45:27,857
I'm gonna keep                  
all this private.               

898
00:45:27,925 --> 00:45:30,259
This is an example of           
making it private first and     

899
00:45:30,328 --> 00:45:33,296
then I'm gonna think about      
what I want to be public.       

900
00:45:33,364 --> 00:45:34,997
You see,                        
the design approach there?      

901
00:45:35,066 --> 00:45:39,802
All right,                      
let's go look at card, so       

902
00:45:39,871 --> 00:45:42,304
here's Card. Card definitely,   
this has to be public.          

903
00:45:42,373 --> 00:45:43,839
We need to know whether         
the cards are face up,          

904
00:45:43,908 --> 00:45:45,908
we, this has to be public.      
Unfortunately,                  

905
00:45:45,977 --> 00:45:48,110
this has to be public.          
Cuz otherwise,                  

906
00:45:48,179 --> 00:45:50,846
we can't tell if two cards      
are the same without that,      

907
00:45:50,915 --> 00:45:54,516
but these two guys definitely   
don't need to be public.        

908
00:45:54,585 --> 00:45:58,620
This whole idea of I, making    
identierFactory that's purely   

909
00:45:58,689 --> 00:46:02,458
internal implementation, okay,  
so no reason for that to be     

910
00:46:04,295 --> 00:46:06,995
public. And this really,        
I'd love this to be private as  

911
00:46:07,064 --> 00:46:09,965
well, because a card it's       
either face up it's matched     

912
00:46:10,034 --> 00:46:12,134
whether it's the same           
as another card,                

913
00:46:12,203 --> 00:46:14,971
I shouldn't have to look        
an identifier to find that.     

914
00:46:15,039 --> 00:46:18,007
I should be able to say the     
this card == the other card,    

915
00:46:18,076 --> 00:46:20,308
wouldn't that be cool?          
And yeah it is cool and         

916
00:46:20,377 --> 00:46:23,646
we're gonna be doing that, in,  
later in this lecture or next   

917
00:46:23,714 --> 00:46:26,582
lecture. Um, this is really     
kind of gross but for now we    

918
00:46:26,650 --> 00:46:28,350
have to leave that public       
because otherwise we do,        

919
00:46:28,419 --> 00:46:31,687
we can't tell what two          
cards are the same. Okay,       

920
00:46:31,756 --> 00:46:35,090
here's the Concentration game,  
this is a really interesting    

921
00:46:35,159 --> 00:46:38,660
case of private and public      
because, here is an object,     

922
00:46:38,729 --> 00:46:41,697
a model that is intended to     
be used by some UI somewhere,   

923
00:46:41,765 --> 00:46:44,500
okay. It's very intentional     
use kind of thing, and          

924
00:46:44,569 --> 00:46:46,535
there's some things             
we know are private,            

925
00:46:46,604 --> 00:46:49,271
like this guy for sure,         
indexOfTheOneAndOnlyFaceUpC-    

926
00:46:49,340 --> 00:46:51,640
ard, we don't need someone      
using us to know that,          

927
00:46:51,709 --> 00:46:53,142
they don't need to know that.   

928
00:46:53,211 --> 00:46:55,944
And in fact, if we left that    
public, someone using us would  

929
00:46:56,013 --> 00:46:58,613
be like when am I supposed      
to set that, I wonder?          

930
00:46:58,682 --> 00:47:01,483
Okay, but it has nothing to do  
with it, it's internal to our   

931
00:47:01,552 --> 00:47:06,488
implementation.                 
Cards has to be public          

932
00:47:06,557 --> 00:47:09,625
because otherwise the UI        
can't display the cards.        

933
00:47:09,694 --> 00:47:12,961
However, cards being            
flipped up and down or          

934
00:47:13,030 --> 00:47:18,200
matching that's my job. So I    
am gonna make this one private  

935
00:47:18,269 --> 00:47:22,405
set, okay, so this is gonna be  
yeah you can look at my cards   

936
00:47:22,473 --> 00:47:25,608
if you wanna use counting       
game but I am responsible for   

937
00:47:25,676 --> 00:47:29,077
setting face up and             
is matched. So                  

938
00:47:29,146 --> 00:47:32,114
you can see this one's          
clearly private set,            

939
00:47:32,183 --> 00:47:35,784
everyone see that? Yeah.        
>> So for that you can access   

940
00:47:35,853 --> 00:47:38,487
the cards but you can't         
access the methods or           

941
00:47:38,556 --> 00:47:40,956
properties associated with it?  
>> Yeah, so                     

942
00:47:41,025 --> 00:47:43,759
the question is when it's       
like this does that mean I      

943
00:47:43,827 --> 00:47:46,962
can access the cards but I      
can't access the methods that   

944
00:47:47,031 --> 00:47:50,366
are on the cards you mean?      
No the methods on the cards,    

945
00:47:50,435 --> 00:47:53,436
that's over,                    
here those are public, okay,    

946
00:47:53,504 --> 00:47:56,905
those are not internal so       
I can access those. From here,  

947
00:47:56,974 --> 00:48:00,542
okay? But you remember that     
this is a value type, so        

948
00:48:00,611 --> 00:48:03,745
I can't set is Space up and     
stuff, I can only set that      

949
00:48:03,814 --> 00:48:07,950
directly in the array. Like     
I'm doing right here. You see,  

950
00:48:08,018 --> 00:48:10,252
here I'm modifying the thing    
in place in the array.          

951
00:48:10,321 --> 00:48:13,121
That's the only way to do it.   
Well, I can't do this if this   

952
00:48:13,190 --> 00:48:17,559
is private set. Okay?           
Cuz this is a value type.       

953
00:48:17,628 --> 00:48:20,796
So this makes it so this, this  
it's kind of like it's a let.   

954
00:48:20,865 --> 00:48:22,731
This almost makes               
it like a let for               

955
00:48:22,800 --> 00:48:25,101
other people, people other      
than me. And then, and so       

956
00:48:25,169 --> 00:48:28,571
you can't touch anything in     
an array when it's a let. So    

957
00:48:28,639 --> 00:48:31,573
that's a really cool            
feature of value types.         

958
00:48:31,642 --> 00:48:33,875
And remember that               
array's a value type and        

959
00:48:33,944 --> 00:48:37,646
card is a value type. So        
that whole thing is frozen for  

960
00:48:37,715 --> 00:48:41,616
people who, you can't be        
modified for outside people.    

961
00:48:41,685 --> 00:48:44,152
But for us,                     
it's private set so             

962
00:48:44,221 --> 00:48:46,789
we can do anything we want      
in there which we have been     

963
00:48:46,857 --> 00:48:50,259
doing. All right. And           
then of course, choose card.    

964
00:48:50,328 --> 00:48:53,929
That's our fundamental public   
API. So we got to leave that    

965
00:48:53,998 --> 00:48:56,298
not private, okay.              
That's how people do it. And    

966
00:48:56,367 --> 00:48:59,869
initializing, initializers can  
be made private as well. But    

967
00:48:59,937 --> 00:49:02,971
this one obviously can't be     
private because otherwise no    

968
00:49:03,040 --> 00:49:06,976
one could create a game, all    
right. So that's it. I really   

969
00:49:07,044 --> 00:49:10,045
got that. Now, while I'm here,  
I'm gonna show you another      

970
00:49:10,114 --> 00:49:12,982
API protection thing that's     
different from access control.  

971
00:49:13,050 --> 00:49:16,618
That's still good, which        
is using assertions, okay.      

972
00:49:16,687 --> 00:49:18,654
Do anyone know what             
an assertion is from other      

973
00:49:18,722 --> 00:49:21,957
languages? An assertion is      
just a function that you call   

974
00:49:22,026 --> 00:49:25,027
where you assert something      
to be true. And if it's not,    

975
00:49:25,095 --> 00:49:28,063
your program crashes and        
print out an error.             

976
00:49:28,131 --> 00:49:31,533
And you put it in your code,    
the asserts are ignored when    

977
00:49:31,602 --> 00:49:33,936
you ship to the App Store. But  
when you're in development,     

978
00:49:34,005 --> 00:49:35,504
it'll be crashing your          
program, which is good,         

979
00:49:35,572 --> 00:49:38,807
cuz it takes the debugger       
right to the assertion failed.  

980
00:49:38,876 --> 00:49:42,477
And asserts are a great way to  
protect your API. For example,  

981
00:49:42,546 --> 00:49:43,979
look at this API, chooseCard.   

982
00:49:44,047 --> 00:49:46,448
What if someone                 
says at index -1?               

983
00:49:46,517 --> 00:49:51,620
Or at index 100 and             
they're only 12 cards.          

984
00:49:51,689 --> 00:49:54,657
Okay, that's gonna crash        
somewhere deep inside here,     

985
00:49:54,726 --> 00:49:56,425
probably like maybe here or     

986
00:49:56,494 --> 00:49:59,694
something like that. And if     
I'm the Google guys again, and  

987
00:49:59,763 --> 00:50:01,363
these guys are in               
another building and            

988
00:50:01,431 --> 00:50:05,900
I accidentally pass -1 here     
and I don't know what's. And    

989
00:50:05,969 --> 00:50:09,438
the crash happens in here, I'm  
gonna need to have this code,   

990
00:50:09,507 --> 00:50:11,807
and look in there,              
and I'm debugging it.           

991
00:50:11,876 --> 00:50:13,842
That code belongs to someone    
in another building,            

992
00:50:13,910 --> 00:50:16,712
why would I ever wanna be in    
here debugging it? Instead,     

993
00:50:16,780 --> 00:50:20,382
the guys in the other building  
should put an assert here.      

994
00:50:20,450 --> 00:50:28,290
That asserts that the cards     
indices contain that index.     

995
00:50:28,359 --> 00:50:31,360
Okay, if the card's indices     
don't contain this index,       

996
00:50:31,429 --> 00:50:34,563
then we're going to crash, if   
we're in development and so,    

997
00:50:34,632 --> 00:50:37,266
then we want to put some        
kind of crash message here.     

998
00:50:37,334 --> 00:50:40,736
I like to put the name of       
the struct or class and         

999
00:50:40,805 --> 00:50:44,739
the function which chooseCard.  
I even like to include          

1000
00:50:44,808 --> 00:50:47,876
the actual arguments that you   
passed so you can see what you  

1001
00:50:47,944 --> 00:50:51,914
passed there and then, I give   
the message. In this case,      

1002
00:50:51,983 --> 00:50:57,186
something like chosen           
index not in the cards.         

1003
00:50:59,523 --> 00:51:02,091
So that, so                     
now if someone calls to choose  

1004
00:51:02,159 --> 00:51:04,860
card at minus one, it's         
gonna crash right away and      

1005
00:51:04,928 --> 00:51:06,695
put that on the console.        
And they're gonna be like,      

1006
00:51:06,763 --> 00:51:08,564
oh, shows the index not         
on the card, oh, and            

1007
00:51:08,632 --> 00:51:11,667
I passed minus one. You see,    
they're gonna one stop shop.    

1008
00:51:11,735 --> 00:51:14,803
Know what they did. And with    
the similar thing thing down    

1009
00:51:14,872 --> 00:51:18,239
here for number of pairs of     
cards because it's illegal to   

1010
00:51:18,308 --> 00:51:22,678
have 0 or less pairs of cards.  
You have to have at least one   

1011
00:51:22,747 --> 00:51:25,514
pair of card. So here I'm just  
gonna have the assertion be     

1012
00:51:25,583 --> 00:51:29,184
that the number of Pairs Of     
Cards is greater than 0.        

1013
00:51:29,253 --> 00:51:30,986
And if there is an error        
then I'm gonna say yes,         

1014
00:51:31,054 --> 00:51:34,890
I'm in the concentrations       
Init and                        

1015
00:51:34,959 --> 00:51:40,629
you passed me this number of    
pairs of cards right here and   

1016
00:51:40,698 --> 00:51:45,100
the problem here is that        
you must have at least          

1017
00:51:45,169 --> 00:51:49,604
one pair of cards. Okay?        
So, you see how I'm, I'm using  

1018
00:51:49,673 --> 00:51:53,476
a search here to kinda protect  
my API against improper use.    

1019
00:51:53,544 --> 00:52:00,282
Question back there? Yeah?      
>> Sorry when you,              

1020
00:52:00,351 --> 00:52:01,616
Sorry when you-                 
>> When would you set init      

1021
00:52:01,685 --> 00:52:02,250
as private?                     
>> Oh, so                       

1022
00:52:02,319 --> 00:52:07,122
the question is when would I    
set my init as private, okay.   

1023
00:52:07,191 --> 00:52:10,826
Well, you might have            
a complicated object that       

1024
00:52:10,895 --> 00:52:14,062
only creates instances          
of itself. For example,         

1025
00:52:14,131 --> 00:52:16,030
with static methods or          
something like that.            

1026
00:52:16,099 --> 00:52:18,600
Or you might have multiple in   
it. Some of which you'll allow  

1027
00:52:18,669 --> 00:52:21,537
other people to call. But some  
of which you call internally    

1028
00:52:21,605 --> 00:52:24,906
to create, okay. You might      
even have public ones that is   

1029
00:52:24,975 --> 00:52:27,409
part of their implementation    
called the private ones. Okay,  

1030
00:52:27,477 --> 00:52:30,312
cuz inits can call each other   
which we'll talk about on       

1031
00:52:30,381 --> 00:52:34,149
Wednesday. So that's why you    
might have some private. Okay,  

1032
00:52:34,218 --> 00:52:36,451
everybody cool with             
access control and              

1033
00:52:36,520 --> 00:52:40,922
assertions? All right,          
back to the slides.             

1034
00:52:40,991 --> 00:52:45,127
Where are we? Here, okay. Cool  
one, all right extensions. So   

1035
00:52:45,195 --> 00:52:49,732
extensions are super powerful.  
They're kind of like            

1036
00:52:49,800 --> 00:52:52,367
a weapon you'll want to be      
careful when you're wielding,   

1037
00:52:52,436 --> 00:52:56,004
because you can go crazy with   
them. And what an extension     

1038
00:52:56,073 --> 00:53:01,176
allows you to do is add vars    
and functions to other classes  

1039
00:53:01,245 --> 00:53:03,378
even if you don't have          
the code to those classes.      

1040
00:53:03,447 --> 00:53:06,681
Even if there in another frame  
work like UI Kits or something  

1041
00:53:06,750 --> 00:53:10,753
like that. So you can add bars  
and methods to it. You can add  

1042
00:53:10,821 --> 00:53:14,389
it to UI Button. You can        
add it UI View Controller.      

1043
00:53:14,458 --> 00:53:17,459
Anything you want. Okay?        
So this is a very, very, very   

1044
00:53:17,528 --> 00:53:21,296
powerful feature. And really    
I'm sure what's swimming about  

1045
00:53:21,364 --> 00:53:23,865
the cap, possibilities is       
nothing compared to the actual  

1046
00:53:23,934 --> 00:53:26,702
possibilities because there     
are other data structures that  

1047
00:53:26,770 --> 00:53:30,105
we haven't even talked about    
that adding an extension to     

1048
00:53:30,173 --> 00:53:33,141
really is powerful and          
we'll get to that by end of     

1049
00:53:33,210 --> 00:53:38,213
Wednesday as well. The basic    
line of it is, is very simple.  

1050
00:53:38,281 --> 00:53:40,949
You just use the keyword        
extension and the name of       

1051
00:53:41,018 --> 00:53:44,319
the structor class you wanna    
add a var property to and       

1052
00:53:44,388 --> 00:53:46,554
then just put the thing         
you want in there.              

1053
00:53:46,623 --> 00:53:51,560
Now, it has one very some       
serious restriction which is    

1054
00:53:51,629 --> 00:53:56,331
that it can have no storage.    
This extension, this code that  

1055
00:53:56,400 --> 00:53:59,300
you're extending this other     
thing, it can have no vars      

1056
00:53:59,369 --> 00:54:01,270
that are storage. It could      
have vars that are computed.    

1057
00:54:01,338 --> 00:54:04,373
But it can't have any           
vars with storage. So           

1058
00:54:04,441 --> 00:54:07,676
that does restrict the kind     
of thing that you can           

1059
00:54:07,745 --> 00:54:11,013
add to a function. Okay,        
but you kinda turn out that     

1060
00:54:11,081 --> 00:54:14,149
restriction is actually a good  
restriction. It's not like      

1061
00:54:14,217 --> 00:54:16,952
the too bad they could          
invent it with storage. You     

1062
00:54:17,020 --> 00:54:19,354
actually don't want storage,    
and you will see as we          

1063
00:54:19,423 --> 00:54:22,690
go along why that is. So, this  
feature as you might imagine    

1064
00:54:22,759 --> 00:54:26,728
is easily abused and the        
number one ways to get abuse,   

1065
00:54:26,797 --> 00:54:29,598
and I encourage you not to      
abuse at this way is you do     

1066
00:54:29,667 --> 00:54:33,835
not want to add a bar or        
a func to class that doesn't    

1067
00:54:33,904 --> 00:54:38,840
make sense for that class.      
It's a real temptation for      

1068
00:54:38,909 --> 00:54:43,578
example for an init or string   
to add a function that has to   

1069
00:54:43,647 --> 00:54:47,916
do with concentration. Some     
concentration specific method   

1070
00:54:47,984 --> 00:54:50,719
you're adding to string cuz     
it'll clean up your code or     

1071
00:54:50,788 --> 00:54:53,689
look nice or whatever But you   
really don't wanna do that.     

1072
00:54:53,757 --> 00:54:56,658
The only method and functions   
you wanna add to string or      

1073
00:54:56,727 --> 00:54:59,962
methods that make string about  
a class. They make it a better  

1074
00:55:00,030 --> 00:55:03,398
string not they make it knows   
about concentration. Now,       

1075
00:55:03,467 --> 00:55:06,134
it's probably possible to       
add string masses to make it    

1076
00:55:06,203 --> 00:55:08,503
know about concentrations that  
nothing really wrong with it.   

1077
00:55:08,572 --> 00:55:10,405
It's just kind of bad design.   
Okay so                         

1078
00:55:10,474 --> 00:55:14,209
this extension's feature like   
I said is very powerful,        

1079
00:55:14,277 --> 00:55:17,979
since you're just beginning     
here, you can think of it at    

1080
00:55:18,048 --> 00:55:21,783
the beginning as just a way     
to add utility, functions and   

1081
00:55:21,852 --> 00:55:24,419
things like that to             
clean up your code.             

1082
00:55:24,488 --> 00:55:27,622
Okay, that the first level of   
learning about extensions so    

1083
00:55:27,691 --> 00:55:29,925
I am going to show you          
how we could do that for        

1084
00:55:29,994 --> 00:55:33,862
example in Concentration. So    
let's go to concentration and   

1085
00:55:33,930 --> 00:55:37,298
use an extension to add         
something interesting and       

1086
00:55:37,367 --> 00:55:41,202
what interesting thing we are   
going to do is we are going to  

1087
00:55:41,271 --> 00:55:43,805
go to our view                  
controller over here and        

1088
00:55:43,874 --> 00:55:47,876
look at this code right here    
which is kind of messy.         

1089
00:55:47,945 --> 00:55:50,245
Right here. Okay?               
What is messy about this code?  

1090
00:55:50,314 --> 00:55:55,150
Well. Okay. All I really wanna  
do is remove a random emoji.    

1091
00:55:55,219 --> 00:55:57,051
And you have to have            
a whole other line of code.     

1092
00:55:57,120 --> 00:56:02,457
And that line of code has this  
horrendous amount of. Changing  

1093
00:56:02,526 --> 00:56:06,328
from unsigned ints to regular   
ints and all that stuff.        

1094
00:56:06,396 --> 00:56:08,930
So it just really looks bad,    
and it's hard to read,          

1095
00:56:08,999 --> 00:56:10,865
it's hard to understand         
what is going in here.          

1096
00:56:10,934 --> 00:56:13,502
I'm having to do so many type   
conversions, stuff like that.   

1097
00:56:13,570 --> 00:56:18,006
It's awful, okay? Really what   
I'd like to do is generate      

1098
00:56:18,075 --> 00:56:24,146
a random number and put it      
right here. So what if int,     

1099
00:56:24,215 --> 00:56:27,916
the type int, had a var         
which gave me a random          

1100
00:56:27,984 --> 00:56:31,319
integer? Okay, that's a very    
int thing, nothing to           

1101
00:56:31,388 --> 00:56:33,822
do with concentration,          
it's just int thing.            

1102
00:56:33,891 --> 00:56:38,126
It gives me a random integer.   
So we're going to extend int    

1103
00:56:38,195 --> 00:56:42,263
to give back a random integer.  
Specifically, we're gonna make  

1104
00:56:42,332 --> 00:56:44,799
it so that when you ask an int  
please give me a random         

1105
00:56:44,868 --> 00:56:47,436
integer it gives a random       
integer between 0 and that      

1106
00:56:47,504 --> 00:56:51,840
int. Okay, so if I say five,    
I can even say, I'm gonna be    

1107
00:56:51,909 --> 00:56:55,143
able to say here let x equal    
five dot random integer.        

1108
00:56:55,212 --> 00:56:58,580
And I'm gonna call this         
thing arc4random, this var.     

1109
00:56:58,649 --> 00:57:01,349
Because I'm gonna use           
arc4random to generate it and   

1110
00:57:01,418 --> 00:57:03,919
people know the semantics       
of arc4random which is          

1111
00:57:03,988 --> 00:57:04,786
a random a number               

1112
00:57:04,854 --> 00:57:08,523
between 0 and another number.   
So this is, I'm gonna make      

1113
00:57:08,592 --> 00:57:13,428
it so this will work and that   
will give me 0, 1, 2, 3, or 4.  

1114
00:57:13,496 --> 00:57:18,634
So how do I do that?            
Extension int and then in here  

1115
00:57:18,702 --> 00:57:24,306
I put this var arc4random.      
I have to say what type it is,  

1116
00:57:24,374 --> 00:57:27,175
it's also gonna be an int.      
It could could be a string or   

1117
00:57:27,244 --> 00:57:29,411
whatever but                    
it's also gonna be an int. And  

1118
00:57:29,479 --> 00:57:33,014
I'm essentially gonna return    
all this mess right here. So    

1119
00:57:33,083 --> 00:57:37,819
I'm just gonna cut that out of  
there. I'm gonna return this.   

1120
00:57:37,888 --> 00:57:40,622
But it's not a random           
number between 0 and            

1121
00:57:40,691 --> 00:57:44,526
emojiChoices.count, it's        
a random order between 0 and    

1122
00:57:44,595 --> 00:57:50,665
what? Yes, whoa, I wish I       
could give extra credit or      

1123
00:57:50,734 --> 00:57:53,201
like Mehran, throwing           
some candy out there or         

1124
00:57:53,270 --> 00:57:56,337
something because yes           
absolutely, it's between 0 and  

1125
00:57:56,406 --> 00:58:01,443
self. Because this is a var in  
int. And so self is the int     

1126
00:58:01,512 --> 00:58:06,514
you sent it to. Which is        
really kind of cool. So now,    

1127
00:58:06,583 --> 00:58:09,784
since int can do this, all we   
need to do right here is we     

1128
00:58:09,853 --> 00:58:13,789
don't need any of this junk up  
here. Instead of randomIndex,   

1129
00:58:13,857 --> 00:58:17,993
we're just gonna say            
emojiChoices.count.arc4random.  

1130
00:58:18,062 --> 00:58:22,664
Okay, so, that cleaned          
up our code a lot. Now,         

1131
00:58:22,733 --> 00:58:25,467
if we were to do something      
like this, and we wanted to     

1132
00:58:25,536 --> 00:58:28,803
be really good programmers,     
we'd look at this and say, hm,  

1133
00:58:28,872 --> 00:58:30,905
what if self is 0?              
Eh, this is not gonna work,     

1134
00:58:30,974 --> 00:58:32,674
cuz arc4rando_uniform           
doesn't work, but               

1135
00:58:32,743 --> 00:58:35,744
what if self is negative?       
Actually, if self were          

1136
00:58:35,812 --> 00:58:38,513
negative, maybe I could do      
a random number between 0 and   

1137
00:58:38,582 --> 00:58:42,684
that negative number. So, I     
might decide, I'm gonna say if  

1138
00:58:42,753 --> 00:58:46,955
self is greater than 0,         
then I'll do this.              

1139
00:58:47,024 --> 00:58:52,026
Else if self is less than 0,    
then I'm gonna almost do this.  

1140
00:58:52,095 --> 00:58:56,865
What I'm gonna do, is I'm       
gonna say return minus this,    

1141
00:58:56,934 --> 00:59:00,202
the absolute value of myself.   
Okay,                           

1142
00:59:00,270 --> 00:59:04,339
abs is just a global function.  
But I could also just say       

1143
00:59:04,408 --> 00:59:06,675
minus self cuz I checked        
to see if it's negative.        

1144
00:59:06,743 --> 00:59:10,345
Or else if self is 0, which     
would be the else case here,    

1145
00:59:10,414 --> 00:59:12,580
then maybe I'll just return 0.  
So if you say, 0,               

1146
00:59:12,649 --> 00:59:15,950
give me a random number,        
it gives you a 0. So here I've  

1147
00:59:16,019 --> 00:59:19,887
made it that this never         
crashes. This doesn't have to   

1148
00:59:19,956 --> 00:59:23,825
be an optional int and it       
gives a reasonable response.    

1149
00:59:23,894 --> 00:59:26,995
See, and that's pretty          
good when you add bars and      

1150
00:59:27,063 --> 00:59:30,632
functions to any class. Now     
you can just via extensions,    

1151
00:59:30,700 --> 00:59:34,302
you want them to have good      
semantics, sensible semantics.  

1152
00:59:34,371 --> 00:59:36,905
And you don't generally don't   
want them to crash which is     

1153
00:59:36,974 --> 00:59:38,607
what this would have            
done otherwise.                 

1154
00:59:38,675 --> 00:59:40,942
If you sent it to -3.           

1155
00:59:41,011 --> 00:59:45,346
Everyone see how this makes     
our code a lot more readable.   

1156
00:59:45,415 --> 00:59:48,083
And how we added something      
that was sensible for int.      

1157
00:59:49,953 --> 00:59:53,755
All right, that's it, let's     
get back to our slides again.   

1158
00:59:55,659 --> 00:59:58,960
Here is our for enum.           
Okay, optionals,                

1159
00:59:59,029 --> 01:00:03,832
the dreaded word optionals.     
So I told you last              

1160
01:00:03,901 --> 01:00:06,701
week that an optional is just   
a regular old type in Swift.    

1161
01:00:06,770 --> 01:00:07,969
In fact it's a enum,            

1162
01:00:08,037 --> 01:00:11,539
an enumeration. So let's learn  
about enum because enum is      

1163
01:00:11,608 --> 01:00:13,909
another thing I wasn't able to  
work it into concentration,     

1164
01:00:13,977 --> 01:00:17,045
although I am gonna work it     
into next week's demo. Okay,    

1165
01:00:17,114 --> 01:00:19,981
our drawing demo. But I want    
to explain what it is so        

1166
01:00:20,050 --> 01:00:22,751
that I can explain what         
optionals are a little better.  

1167
01:00:22,820 --> 01:00:25,753
So an enum is just like         
an enum in other languages.     

1168
01:00:25,822 --> 01:00:28,156
It's a data type,               
just like struct is a type or   

1169
01:00:28,225 --> 01:00:29,824
class is a type,                
enum is a type.                 

1170
01:00:29,893 --> 01:00:32,828
Exactly the same, you can use   
it in exactly the same places.  

1171
01:00:32,896 --> 01:00:37,899
It's just that it has only      
discrete values. Here's         

1172
01:00:37,968 --> 01:00:40,701
a FastFoodMenuItem enum, it     
can only be hamburger, fries,   

1173
01:00:40,770 --> 01:00:43,471
drink, or cookie. That's it,    
it can't be anything else       

1174
01:00:43,540 --> 01:00:45,172
besides one of those            
four things, so                 

1175
01:00:45,241 --> 01:00:50,645
that's what an enum is. Enums   
are value types, like structs,  

1176
01:00:50,714 --> 01:00:55,783
they get copied as you pass     
them around. Now enums in       

1177
01:00:55,852 --> 01:01:00,488
Swift little bit more powerful  
then your typical enum because  

1178
01:01:00,556 --> 01:01:05,026
each case can also have what's  
called associated data, or      

1179
01:01:05,094 --> 01:01:08,296
an associated value.            
So in my fast food item one my  

1180
01:01:08,365 --> 01:01:10,565
hamburgers have                 
the number of patties,          

1181
01:01:10,634 --> 01:01:12,400
is it a double burger or        
a triple or                     

1182
01:01:12,469 --> 01:01:15,303
a single? The fries has         
the size of the fries,          

1183
01:01:15,371 --> 01:01:18,773
a large fry, or a small. And    
I've even used another enum,    

1184
01:01:18,842 --> 01:01:20,842
you see down here               
at the bottom.                  

1185
01:01:20,911 --> 01:01:24,245
I have another, oops, my        
thing work here. There it is.   

1186
01:01:24,314 --> 01:01:29,250
This is not very good. Okay,    
we got it. There it is. So      

1187
01:01:29,319 --> 01:01:32,153
I can use another enum there    
to do the size of it and        

1188
01:01:32,222 --> 01:01:37,058
then drink. It has two          
pieces of associated data.      

1189
01:01:37,127 --> 01:01:39,160
Okay, let's see if we can       
get this working for that.      

1190
01:01:39,229 --> 01:01:41,062
And if you look at its two      
pieces of associated data,      

1191
01:01:41,130 --> 01:01:42,097
look at the first one.          

1192
01:01:42,165 --> 01:01:45,499
That string, it has no name.    
These other ones have names,    

1193
01:01:45,568 --> 01:01:47,969
like number of patties, size,   
this one has no name for        

1194
01:01:48,038 --> 01:01:50,705
the first one, it does have     
a name for the second one.      

1195
01:01:50,774 --> 01:01:53,374
First the strings and then an   
int. Now the names here don't   

1196
01:01:53,443 --> 01:01:56,544
matter that much because when   
we extract this information,    

1197
01:01:56,613 --> 01:01:59,246
we're gonna be able to give     
it our own name anyway,         

1198
01:01:59,315 --> 01:02:02,350
kind of like tuples. In fact,   
these look a lot like tuples,   

1199
01:02:02,419 --> 01:02:04,552
don't they?                     
These little associated datas,  

1200
01:02:04,620 --> 01:02:07,055
they're kind of like tuples     
because you can have as many    

1201
01:02:07,124 --> 01:02:08,990
of them as you want,            
you specify the type,           

1202
01:02:09,059 --> 01:02:11,093
they have names,                
they're super simple, and       

1203
01:02:11,161 --> 01:02:14,095
they look very much like        
tuples. So, anyway,             

1204
01:02:14,164 --> 01:02:16,697
so this is what it looks        
like to declare an enum with    

1205
01:02:16,766 --> 01:02:20,334
associated data. Now,           
how do you assign an enum?      

1206
01:02:20,403 --> 01:02:23,071
So here is two variables,       
one called menu item,           

1207
01:02:23,140 --> 01:02:25,840
one called other item. They     
are of type FastFoodMenuItem,   

1208
01:02:25,909 --> 01:02:28,876
that's their type. And so       
I set them just by saying       

1209
01:02:28,945 --> 01:02:31,779
FastFoodMenuItem dot            
the case I want.                

1210
01:02:31,848 --> 01:02:37,118
And if it has associated data,  
I have to provide it.           

1211
01:02:37,187 --> 01:02:42,057
So the only time you can set    
the associated data of an enum  

1212
01:02:42,125 --> 01:02:45,226
is when you assign it.          
That's the only time. Okay,     

1213
01:02:45,294 --> 01:02:48,062
you can't go back later and     
change this to be a triple,     

1214
01:02:48,131 --> 01:02:51,032
because this is fundamentally   
a double burger.                

1215
01:02:51,101 --> 01:02:53,634
That's what it is. And it's     
never, if it changed, it would  

1216
01:02:53,703 --> 01:02:56,871
change into a completely        
different thing. All right, so  

1217
01:02:56,940 --> 01:03:01,008
you don't change the patties,   
got that? All right, so, when   

1218
01:03:01,077 --> 01:03:04,980
you're setting these values by  
the way of course you can use   

1219
01:03:05,048 --> 01:03:08,683
type inference, but only on     
one side of that equals. So     

1220
01:03:08,752 --> 01:03:12,354
you could say menuItem equals   
FastFoodMenuItem.hamburger.     

1221
01:03:12,422 --> 01:03:15,089
Which was what was on           
the previous slide, or          

1222
01:03:15,158 --> 01:03:18,626
you could say otherItem of      
type FastFoodMenuItem equals    

1223
01:03:18,695 --> 01:03:19,727
.cookie. You see,               

1224
01:03:19,796 --> 01:03:21,996
I've just basically moved the   
type to the other side. But     

1225
01:03:22,065 --> 01:03:25,966
you can't say yet another item  
equals .cookie. Swift doesn't   

1226
01:03:26,035 --> 01:03:29,337
know enough there to infer the  
type on the other side. There   

1227
01:03:29,406 --> 01:03:31,505
could be other enums with       
.cookie in it, for example,     

1228
01:03:31,574 --> 01:03:33,775
that you might add later. And   
then all of a sudden your code  

1229
01:03:33,844 --> 01:03:35,309
won't compile because           
it doesn't know. So             

1230
01:03:35,378 --> 01:03:38,680
it just says from the start,    
I don't know what that is.      

1231
01:03:39,783 --> 01:03:42,350
Now how do you check            
what an enum is?                

1232
01:03:42,419 --> 01:03:44,953
You do not use equals.          
So you don't say,               

1233
01:03:45,021 --> 01:03:49,523
if this menu item equals a      
hamburger then whatever, okay,  

1234
01:03:49,592 --> 01:03:53,328
you do not use equals, you use  
switch. Again, other languages  

1235
01:03:53,397 --> 01:03:56,097
have switch. Switch is          
more powerful in Swift.         

1236
01:03:56,166 --> 01:03:58,900
This is the basic use of        
switch right here, where I'm    

1237
01:03:58,968 --> 01:04:02,137
just looking at every possible  
case that it could be, and      

1238
01:04:02,205 --> 01:04:03,938
if it's that case,              
I do a little bit of code.      

1239
01:04:04,007 --> 01:04:07,041
So here I'm just printing out   
what the various cases are so   

1240
01:04:07,110 --> 01:04:09,043
if it's hamburgers,             
for example,                    

1241
01:04:09,112 --> 01:04:11,379
you can see that I'm            
printing burger.                

1242
01:04:11,448 --> 01:04:14,249
Notice that I'm ignoring the    
associated data here which is   

1243
01:04:14,317 --> 01:04:15,249
perfectly fine.                 

1244
01:04:15,318 --> 01:04:17,886
You're allowed to completely    
ignore the associated data      

1245
01:04:17,955 --> 01:04:21,555
when you're checking            
the state with switch. Now      

1246
01:04:21,624 --> 01:04:25,326
switch requires you to address  
every single case. You are not  

1247
01:04:25,395 --> 01:04:28,463
allowed to look at only two     
of the cases. But, of course,   

1248
01:04:28,531 --> 01:04:34,068
it's got something that can     
help you with that. Oh yes,     

1249
01:04:34,137 --> 01:04:37,605
by the way, you see I've taken  
away the FastFoodMenuItem.,     

1250
01:04:37,674 --> 01:04:40,775
in front of hamburger, fries,   
drink, and coke. Becuase swift  

1251
01:04:40,843 --> 01:04:43,077
can infer that, you're          
switching on a menu item, so    

1252
01:04:43,146 --> 01:04:45,280
it knows this is                
a FastFoodMenuItem, so          

1253
01:04:45,348 --> 01:04:49,317
you can take those away. All    
right, so if you have one of    

1254
01:04:49,385 --> 01:04:52,287
the cases, and you don't wanna  
do anything, you can just       

1255
01:04:52,356 --> 01:04:55,890
break. Break means break        
out of this switch. So          

1256
01:04:55,958 --> 01:04:58,626
that's a way to do nothing in   
this case. So, right here,      

1257
01:04:58,694 --> 01:05:01,062
this code, we print nothing     
because the hamburger case,     

1258
01:05:01,130 --> 01:05:03,698
the menu item is a hamburger    
with two patties, and           

1259
01:05:03,767 --> 01:05:04,999
that hamburger case             
does nothing, so                

1260
01:05:05,068 --> 01:05:08,636
we'll just break out and        
do nothing. Similarly,          

1261
01:05:08,705 --> 01:05:12,306
if you want to do something     
for all the rest of the cases,  

1262
01:05:12,375 --> 01:05:13,841
like here I only want           
to do something for             

1263
01:05:13,910 --> 01:05:16,977
hamburger and fries. Actually   
I do nothing for hamburger and  

1264
01:05:17,046 --> 01:05:18,079
I do something for fries.       

1265
01:05:18,147 --> 01:05:20,949
In all other cases, I just      
want to print other, then you   

1266
01:05:21,017 --> 01:05:24,919
can use default instead of      
case whatever. Now in switch,   

1267
01:05:24,987 --> 01:05:29,424
you can switch any type, you    
can even switch on a string.    

1268
01:05:29,492 --> 01:05:32,426
But if you switch on a string,  
you'd have to have case A,      

1269
01:05:32,495 --> 01:05:35,029
case B, case C, case AA,        
case AB, you see what I mean?   

1270
01:05:35,098 --> 01:05:37,165
You'd have to have every        
case in the world.              

1271
01:05:37,234 --> 01:05:40,502
So of course you're going to    
use default ion a string case   

1272
01:05:40,570 --> 01:05:41,836
switch case the couple          

1273
01:05:41,904 --> 01:05:45,306
ones you wanna case, then you   
would default the rest. So      

1274
01:05:45,375 --> 01:05:50,778
default is a must even for      
enums we use it quite a bit,    

1275
01:05:50,847 --> 01:05:53,948
all right? So                   
that's break an enum. So        

1276
01:05:54,017 --> 01:05:58,753
if this were a cookie then it   
would print other. All right,   

1277
01:05:58,822 --> 01:06:01,455
multiple lines, I just wanted   
to make clear that, multiple    

1278
01:06:01,524 --> 01:06:03,724
lines of code are allowed, it   
doesn't have to be one line.    

1279
01:06:03,793 --> 01:06:05,025
That was just cuz               
I'm on slides here,             

1280
01:06:05,094 --> 01:06:06,661
I'm trying to make              
everything fit, and             

1281
01:06:06,730 --> 01:06:10,265
there's no fall through. So     
in this case, I've got fries,   

1282
01:06:10,333 --> 01:06:12,166
you see up there at the top,    
fries,                          

1283
01:06:12,234 --> 01:06:13,701
large fries there. And          

1284
01:06:13,770 --> 01:06:18,039
so this code would print out    
yummy fires and that's it. So   

1285
01:06:18,107 --> 01:06:20,007
I have multiple lines of        
code in there under fries,      

1286
01:06:20,076 --> 01:06:22,977
two lines of code, and it does  
not fall through and do drink,  

1287
01:06:23,046 --> 01:06:26,080
like in other languages. In C,  
things fall through, in switch  

1288
01:06:26,149 --> 01:06:28,116
but they don't fall through     
here. There is a keyword        

1289
01:06:28,184 --> 01:06:30,585
called fallthrough that would   
let you fall through, but       

1290
01:06:30,653 --> 01:06:36,591
by default it doesn't.          
By the way that it inferred     

1291
01:06:36,660 --> 01:06:40,561
the type all along in here,     
it can for that type as well.   

1292
01:06:40,630 --> 01:06:45,066
I don't have to say             
size,fries size enum.large,     

1293
01:06:45,135 --> 01:06:47,902
I can just say, .large because  
it knows that the associated    

1294
01:06:47,971 --> 01:06:53,274
data of fries is s              
fries size enum. Okay,          

1295
01:06:53,342 --> 01:06:57,778
now, what if I want to get      
the associated data. So I do,   

1296
01:06:57,847 --> 01:07:00,815
I am interested in it. We do    
that with switch as well,       

1297
01:07:00,883 --> 01:07:05,319
we just do this little let      
business. See the little lets.  

1298
01:07:05,388 --> 01:07:07,789
In all the cases that you       
want this associated data,      

1299
01:07:07,858 --> 01:07:09,190
you don't have to do            
it in all cases, but            

1300
01:07:09,258 --> 01:07:11,326
in the ones you want it? You    
just say, open parentheses,     

1301
01:07:11,394 --> 01:07:15,229
let and a name of a little      
local variable for              

1302
01:07:15,298 --> 01:07:18,265
each of the associated          
pieces of data. Now,            

1303
01:07:18,334 --> 01:07:21,702
that little name that you use,  
so if this were a coke see it   

1304
01:07:21,771 --> 01:07:25,306
would print whatever ounces     
coke right there, cuz just      

1305
01:07:25,374 --> 01:07:28,409
getting the Coke into brand.    
It's getting the ounces into    

1306
01:07:28,477 --> 01:07:31,145
something called ounces, and    
then it's doing that print.     

1307
01:07:31,214 --> 01:07:35,716
This naming does not            
have to be the same names       

1308
01:07:35,785 --> 01:07:38,419
as you declared the enum from.  
In fact,                        

1309
01:07:38,487 --> 01:07:42,723
if we look at this Coke one     
right here, this let brand,     

1310
01:07:42,792 --> 01:07:45,827
remember in the original enum   
that didn't even have a name,   

1311
01:07:45,896 --> 01:07:48,929
it was just a string, right?    
And it had ounces,              

1312
01:07:48,998 --> 01:07:52,399
colon ounces, and up here       
with hamburger, pattyCount,     

1313
01:07:52,468 --> 01:07:56,837
that was called patties in      
the original declaration. So    

1314
01:07:56,906 --> 01:08:00,641
again, does this not look       
familiar to tuples, right?      

1315
01:08:00,710 --> 01:08:03,878
You can rename them when        
you're getting the information  

1316
01:08:03,946 --> 01:08:07,549
out of them. So                 
this is how you extract data    

1317
01:08:07,617 --> 01:08:11,953
out of the associated types.    
Very simple, and                

1318
01:08:12,022 --> 01:08:14,756
again it's optional you         
don't have to have it there.    

1319
01:08:15,992 --> 01:08:19,126
Also enums, they're like        
structs and classes.            

1320
01:08:19,195 --> 01:08:23,431
They can have methods and they  
can have vars, but no storage.  

1321
01:08:23,500 --> 01:08:26,600
All the stories of an enum      
is in which case it is and      

1322
01:08:26,669 --> 01:08:28,035
that case is associated data.   

1323
01:08:28,104 --> 01:08:30,872
That's it, you can't have many  
other vars or anything else.    

1324
01:08:30,940 --> 01:08:34,275
So the only vars you could      
have are computed vars.         

1325
01:08:34,344 --> 01:08:37,245
So see the example I have       
here where it's calories,       

1326
01:08:37,313 --> 01:08:40,148
where you'd compute             
the calories of that menu item  

1327
01:08:40,216 --> 01:08:43,618
that would have to be           
a computed type. Can't store    

1328
01:08:43,686 --> 01:08:47,422
anything in an enum except for  
the associated data right       

1329
01:08:47,490 --> 01:08:50,291
there. Now if you're writing    
a func like this one,           

1330
01:08:50,360 --> 01:08:53,495
isIncludedInSpecialOrder        
number one or number two or     

1331
01:08:53,563 --> 01:08:56,164
whatever. If you're             
doing that, then you can        

1332
01:08:56,232 --> 01:09:01,336
get your own associated         
data using switch on self.      

1333
01:09:01,404 --> 01:09:03,972
Cuz I'm inside the enum to      
permutation here, right?        

1334
01:09:04,040 --> 01:09:05,573
So I can switch on self,        
and then,                       

1335
01:09:05,642 --> 01:09:07,241
I could get my                  
associated data out so          

1336
01:09:07,310 --> 01:09:08,743
I can calculate my calories.    
Or                              

1337
01:09:08,811 --> 01:09:11,445
in this case, I'm calculating   
whether the hamburger with      

1338
01:09:11,514 --> 01:09:14,015
two patties is included in      
special order number two.       

1339
01:09:14,084 --> 01:09:17,285
And my code here says           
yes because pretty much,        

1340
01:09:17,353 --> 01:09:19,120
special order number            
one is a single burger,         

1341
01:09:19,189 --> 01:09:21,789
and/or number two is a double.  
Now there's some other          

1342
01:09:21,858 --> 01:09:24,358
interesting things to look      
at in this code. Notice that    

1343
01:09:24,427 --> 01:09:27,629
fries and cookie right there.   
Right in the middle, fries and  

1344
01:09:27,697 --> 01:09:31,565
cookie. Those I combine         
them into one case,             

1345
01:09:31,634 --> 01:09:34,468
which that's allowed with       
commas you can have multiple    

1346
01:09:34,537 --> 01:09:38,206
going on there.                 
Also noticing drink, okay, I'm  

1347
01:09:38,274 --> 01:09:41,042
getting the number of ounces    
in a drink but evidently in     

1348
01:09:41,110 --> 01:09:44,145
a special order you can have    
any drink that's 16 ounces.     

1349
01:09:44,214 --> 01:09:47,314
So I don't care what kind of    
drink it is, I don't care for   

1350
01:09:47,383 --> 01:09:51,152
that brand. So I use the        
universal i don't care symbol   

1351
01:09:51,221 --> 01:09:54,722
in Swift which is under bar,    
right? Remember, we used        

1352
01:09:54,791 --> 01:09:58,359
underbar when we didn't care    
what the external name and      

1353
01:09:58,427 --> 01:10:01,662
touch card was. We used it in   
a four loop when we didn't      

1354
01:10:01,731 --> 01:10:04,065
care what the identifier was    
anymore in concentration,       

1355
01:10:04,134 --> 01:10:07,535
so we can use it here as well,  
all right?                      

1356
01:10:09,239 --> 01:10:14,074
You can modify self in an enum  
as long as it's in a var. If    

1357
01:10:14,143 --> 01:10:17,845
it's modifiable, you just say   
self equals some other case.    

1358
01:10:17,914 --> 01:10:19,847
And if that other case          
requires associated data,       

1359
01:10:19,915 --> 01:10:23,083
you'll have to provide it       
then, you can say self equals.  

1360
01:10:23,152 --> 01:10:25,720
Now, a very important thing to  
notice here, if you're going    

1361
01:10:25,789 --> 01:10:28,890
to modify yourself in an enum   
by saying self equals,          

1362
01:10:28,959 --> 01:10:30,357
that's the only way             
to modify yourself,             

1363
01:10:30,426 --> 01:10:34,195
by the way.                     
Then you have to put mutating   

1364
01:10:34,264 --> 01:10:37,197
in front of the function        
that mutates you,               

1365
01:10:37,266 --> 01:10:38,566
that modifies self.             

1366
01:10:38,634 --> 01:10:43,304
That's because fast enum        
is a value type and             

1367
01:10:43,372 --> 01:10:46,073
remember the value types are    
passed around by copying but    

1368
01:10:46,142 --> 01:10:49,810
there is copy on write. So if   
it doesn't copy on write which  

1369
01:10:49,879 --> 01:10:52,546
means it doesn't actually       
make a copy until you write.    

1370
01:10:52,615 --> 01:10:53,615
Well if it's gonna do that,     

1371
01:10:53,683 --> 01:10:58,519
it needs to know which          
funcs might write. So           

1372
01:10:58,588 --> 01:11:01,388
that's what mutating means, it  
means this func might write,    

1373
01:11:01,457 --> 01:11:05,025
it might change this. You have  
to do exactly the same thing    

1374
01:11:05,094 --> 01:11:08,996
in a struct. If you have        
a func in a struct, and         

1375
01:11:09,064 --> 01:11:10,965
it modifies any                 
internal state of               

1376
01:11:11,033 --> 01:11:13,100
the struct, it has to           
be marked mutating, so          

1377
01:11:13,169 --> 01:11:16,370
the Swift knows to copy and     
write. And not to worry, Swift  

1378
01:11:16,439 --> 01:11:19,440
is super smart, it'll see your  
code, it'll see you're saying   

1379
01:11:19,508 --> 01:11:22,142
self equal, it'll see that      
you're modifying your bars in   

1380
01:11:22,211 --> 01:11:26,046
a struct And it will complain   
and say this is protected you   

1381
01:11:26,115 --> 01:11:29,183
can't write to this thing coz   
this is not a mutating func.    

1382
01:11:29,251 --> 01:11:31,418
And you can fix it by           
making it mutating and          

1383
01:11:31,487 --> 01:11:34,555
in fact you can see that        
concentration demo in a second  

1384
01:11:34,624 --> 01:11:37,758
here. All right so let's see    
if for enums, very simple.      

1385
01:11:37,826 --> 01:11:41,562
So an optional then is just     
an enum, it looks like this,    

1386
01:11:41,631 --> 01:11:44,398
kind of, conceptually.          
It's an optional,               

1387
01:11:44,467 --> 01:11:47,435
it's a generic type like array  
is. Array can have anything in  

1388
01:11:47,504 --> 01:11:49,103
it, an optional can             
be an optional Int,             

1389
01:11:49,172 --> 01:11:51,739
an optional string, whatever    
it's a generic type. And        

1390
01:11:51,808 --> 01:11:53,941
it has two cases in the enum,   

1391
01:11:54,009 --> 01:11:58,713
the case none which is not      
set, nill, and the other case   

1392
01:11:58,781 --> 01:12:01,782
some in which it has some       
associated data of that type.   

1393
01:12:01,851 --> 01:12:04,352
So an optional int that would   
mean int, so that's it,         

1394
01:12:04,420 --> 01:12:07,588
that's what an optional is.     
Now an optional, Why don't,     

1395
01:12:07,657 --> 01:12:09,190
why didn't we just              
leave it in enum?               

1396
01:12:09,259 --> 01:12:10,624
Well, God, can you imagine,     

1397
01:12:10,693 --> 01:12:13,360
every time you wanna unwrap     
an optional, you're having to   

1398
01:12:13,429 --> 01:12:16,029
switch on that thing in case    
some get the associated data?   

1399
01:12:16,098 --> 01:12:18,866
That would be so much typing.   
So all of these special         

1400
01:12:18,935 --> 01:12:21,135
characters we have              
are optionals, question marks,  

1401
01:12:21,204 --> 01:12:23,470
exclamation points, ifs,        
double question marks.          

1402
01:12:23,539 --> 01:12:26,674
All that stuff is just so that  
we don't have to be constantly  

1403
01:12:26,743 --> 01:12:29,877
switching on our optional and   
doing case this, case that.     

1404
01:12:29,945 --> 01:12:31,812
But that's all it's             
doing under the covers,         

1405
01:12:31,881 --> 01:12:33,781
it's just syntactic sugar       
that is doing that.             

1406
01:12:33,850 --> 01:12:35,382
It's not doing anything else,   

1407
01:12:35,451 --> 01:12:39,019
it's not, nothing special. And  
so I'm gonna show you what all  

1408
01:12:39,088 --> 01:12:42,189
these special characters        
look like in enum land.         

1409
01:12:42,258 --> 01:12:44,759
And, and I'm even gonna         
show you a new enum or          

1410
01:12:44,827 --> 01:12:47,428
a new optional thing, which     
is this thing at the bottom     

1411
01:12:47,497 --> 01:12:50,497
called optional chaining. And   
it's where you use a single     

1412
01:12:50,566 --> 01:12:52,900
question mark when you're       
accessing an optional.          

1413
01:12:52,969 --> 01:12:55,436
Which that's the one thing we   
have not seen, and I'm gonna    

1414
01:12:55,505 --> 01:12:57,605
show you how that works by      
showing you in enum land.       

1415
01:12:57,673 --> 01:13:02,477
All right? So, declaring        
optionals, obvious, right?      

1416
01:13:02,545 --> 01:13:04,412
If I say hello,                 
which is an optional string,    

1417
01:13:04,481 --> 01:13:08,181
that's just optional angle      
brackets string. And            

1418
01:13:08,250 --> 01:13:11,485
remember that optionals always  
start out nil. So, I'm gonna,   

1419
01:13:11,554 --> 01:13:15,990
it's gonna start out none.      
Couldn't be simpler.            

1420
01:13:16,059 --> 01:13:18,959
Unwrapping, also very simple,   
that's just switching           

1421
01:13:19,028 --> 01:13:22,063
on the thing. So, if I have an  
optional string hello, and I    

1422
01:13:22,131 --> 01:13:25,366
say print(hello!), exclamation  
point to unwrap it,             

1423
01:13:25,435 --> 01:13:27,834
I'm just switching on hello.    
And if it's in the none case,   

1424
01:13:27,903 --> 01:13:30,438
I crash. And                    
if it's in the some case,       

1425
01:13:30,506 --> 01:13:33,240
then I print whatever the       
associated data is. Same thing  

1426
01:13:33,309 --> 01:13:36,577
down with if let at the bottom  
there. I'm switching on hello.  

1427
01:13:36,645 --> 01:13:38,445
If it's in the some case,       
I do it.                        

1428
01:13:38,514 --> 01:13:39,413
If it's in the none case,       

1429
01:13:39,481 --> 01:13:44,619
I do the else part of the if.   
Everybody got that?             

1430
01:13:44,687 --> 01:13:47,188
Implicitly unwrapped optionals  
are exactly the same. It's      

1431
01:13:47,256 --> 01:13:49,956
just that when I say print      
hello over here on this side,   

1432
01:13:50,025 --> 01:13:53,193
this print hello, I don't have  
to put the exclamation point.   

1433
01:13:53,262 --> 01:13:57,731
And it still switches on hello  
and crashes if it's none. So    

1434
01:13:57,800 --> 01:14:01,168
that's implicitly unwrapped.    
Those start out as nil too      

1435
01:14:01,236 --> 01:14:04,105
because they're just            
optionals. The nil-coalescing   

1436
01:14:04,173 --> 01:14:06,340
operator, which is that         
defaulting thing we used,       

1437
01:14:06,409 --> 01:14:09,076
if you remember, in our code.   
We looked in our emoji          

1438
01:14:09,145 --> 01:14:11,245
dictionary, and                 
if it wasn't there,             

1439
01:14:11,313 --> 01:14:14,081
then we returned question       
mark. That's just               

1440
01:14:14,150 --> 01:14:16,918
switching on it. And if it's    
in the case none, then it uses  

1441
01:14:16,986 --> 01:14:19,386
the default, okay, the thing    
on the other side. And          

1442
01:14:19,455 --> 01:14:24,125
if it's in the case some, then  
it uses the thing it found.     

1443
01:14:24,193 --> 01:14:27,861
This is optional chaining.      
So optional chaining, imagine   

1444
01:14:27,930 --> 01:14:31,065
right here, okay, if you look   
at this little let x equal,     

1445
01:14:31,134 --> 01:14:34,635
imagine that x and              
the method foo and              

1446
01:14:34,704 --> 01:14:39,040
the var bar, all three of       
those, imagine those return     

1447
01:14:39,108 --> 01:14:42,476
an optional string. Okay, so    
we don't know what they do,     

1448
01:14:42,545 --> 01:14:43,878
but they return                 
an optional string.             

1449
01:14:43,946 --> 01:14:46,913
They may or may not return      
nil. Okay, well, what optional  

1450
01:14:46,982 --> 01:14:49,350
chaining there allows us to     
do is to call those thing,      

1451
01:14:49,418 --> 01:14:50,985
things in sequence called one.  
And                             

1452
01:14:51,053 --> 01:14:53,320
then when we get the value,     
call the next thing on that.    

1453
01:14:53,389 --> 01:14:55,523
And we get the value, call      
the next thing on that. And     

1454
01:14:55,591 --> 01:14:58,525
if at any time any of those     
things is nil, we just bail     

1455
01:14:58,594 --> 01:15:02,796
out and return nil. So the way  
that works in optional land is  

1456
01:15:02,865 --> 01:15:06,634
we switch on that first.        
If it's none, we return nil.    

1457
01:15:06,703 --> 01:15:09,637
But if it's not,                
we get the data and call foo.   

1458
01:15:09,705 --> 01:15:12,139
If that works, we get the,      
that data from foo, and         

1459
01:15:12,208 --> 01:15:14,475
we call bar.                    
And then eventually,            

1460
01:15:14,543 --> 01:15:17,311
we set y equal to z that        
comes out of that, right?       

1461
01:15:17,380 --> 01:15:20,581
We're just moving across        
the chain. If, at any time,     

1462
01:15:20,649 --> 01:15:22,883
any of those things is nil,     
look at all the case nones.     

1463
01:15:22,951 --> 01:15:25,486
Case .none, case .none, case    
.none, y gets to be nil, and    

1464
01:15:25,554 --> 01:15:28,322
we're done and move along.      
Okay, so that's optional        

1465
01:15:28,390 --> 01:15:32,493
chaining. I made it optional,   
no pun intended, for            

1466
01:15:32,561 --> 01:15:35,462
you to read about that in       
your current assignment.        

1467
01:15:35,531 --> 01:15:38,532
I recommend you do because you  
can make really beautiful code  

1468
01:15:38,601 --> 01:15:41,835
using optional chaining.        
It's really nice.               

1469
01:15:41,904 --> 01:15:46,273
Okay, so we're gonna finish up  
today with a little review and  

1470
01:15:46,342 --> 01:15:49,910
a look forward to the data      
structures to use to build      

1471
01:15:49,979 --> 01:15:54,548
an app in Swift.                
These are the four, class,      

1472
01:15:54,616 --> 01:15:57,451
struct, enum, and protocol.     
Protocol is the new one that    

1473
01:15:57,519 --> 01:16:01,055
I'm gonna talk about starting   
on Wednesday. So a class,       

1474
01:16:01,124 --> 01:16:04,458
as we know, supports            
an object-oriented design.      

1475
01:16:04,526 --> 01:16:07,060
It has single inheritance of    
both functionality and data.    

1476
01:16:07,129 --> 01:16:09,563
You inherit the data,           
your vars.                      

1477
01:16:09,632 --> 01:16:13,667
Stored vars get inherited, um,  
as well as all your methods     

1478
01:16:13,736 --> 01:16:17,939
and stuff. It's a reference     
type, lives in the heap.        

1479
01:16:18,007 --> 01:16:20,073
Now one thing we didn't         
talk about, though,             

1480
01:16:20,142 --> 01:16:23,510
this class lives in the heap.   
When does it get cleaned up     

1481
01:16:23,579 --> 01:16:28,048
out of the heap? And how does   
that happen? Okay, so yeah, so  

1482
01:16:28,117 --> 01:16:30,016
if, people who are coming from  
Java, you're probably like,     

1483
01:16:30,085 --> 01:16:32,919
oh, garbage collection maybe?   
Okay, um, but no, okay,         

1484
01:16:32,988 --> 01:16:35,722
Swift does not use              
garbage collection.             

1485
01:16:35,791 --> 01:16:40,528
It uses a very awesome system   
called reference counting. And  

1486
01:16:40,596 --> 01:16:42,329
in fact, it's automatic         
reference counting,             

1487
01:16:42,397 --> 01:16:44,965
it's all handled for you.       
So how does reference counting  

1488
01:16:45,034 --> 01:16:47,434
work? Okay, we need to talk     
a little bit about that.        

1489
01:16:47,503 --> 01:16:51,739
So let's take a little detour   
here. By the way, examples of   

1490
01:16:51,807 --> 01:16:54,809
classes that we've seen of      
course are UI view controller,  

1491
01:16:54,877 --> 01:16:57,845
view controller, which is our   
subclass of it, UI button,      

1492
01:16:57,914 --> 01:17:00,614
UI label, concentration,        
we made that a class. Those     

1493
01:17:00,682 --> 01:17:03,150
are all classes, not structs,   
right? All right, so let's      

1494
01:17:03,219 --> 01:17:05,786
talk about how this automatic   
reference counting thing        

1495
01:17:05,854 --> 01:17:09,389
works. It's really simple,      
every time, somehow magically,  

1496
01:17:09,458 --> 01:17:13,227
every time that you create a    
pointer to a reference type in  

1497
01:17:13,295 --> 01:17:17,665
the heap, Swift adds one to     
some counter somewhere. And     

1498
01:17:17,733 --> 01:17:22,035
every time that pointer to      
it goes out of scope or         

1499
01:17:22,104 --> 01:17:24,371
is not pointed to it anymore,   
like it was an optional,        

1500
01:17:24,440 --> 01:17:26,072
it got set to nil,              
for example,                    

1501
01:17:26,141 --> 01:17:29,676
then it decrements that count.  
And when that count goes to 0,  

1502
01:17:29,745 --> 01:17:32,580
it takes it out of the heap     
instantly. It's not like        

1503
01:17:32,648 --> 01:17:34,614
it's keeping track, and         
it's doing any marking and      

1504
01:17:34,683 --> 01:17:37,250
sweeping, like a garbage        
collection. It actually         

1505
01:17:37,319 --> 01:17:40,453
instantly removes it as soon    
as no one points to it. So      

1506
01:17:40,522 --> 01:17:42,689
it couldn't be simpler, it's    
exact way you would think,      

1507
01:17:42,758 --> 01:17:44,291
conceptually, to make it work.  

1508
01:17:44,360 --> 01:17:47,861
It's actually quite difficult   
under the covers to do that.    

1509
01:17:47,930 --> 01:17:50,097
Swift was designed with         
it in mind from start.          

1510
01:17:50,165 --> 01:17:55,069
So it's an awesome system.      
You can influence               

1511
01:17:55,138 --> 01:17:57,104
this automatic reference        
counting a little bit.          

1512
01:17:57,172 --> 01:17:59,807
You can't really control it,    
but you can influence,          

1513
01:17:59,875 --> 01:18:02,409
with these three key words      
when you declare a var,         

1514
01:18:02,477 --> 01:18:04,612
okay, a strong,                 
weak, and unowned.              

1515
01:18:04,680 --> 01:18:08,081
These are the three kind        
of influencers you can do.      

1516
01:18:08,150 --> 01:18:11,151
The first one, strong,          
is normal reference counting.   

1517
01:18:11,220 --> 01:18:15,522
So that just means if there's   
a, this pointer is strong, and  

1518
01:18:15,590 --> 01:18:19,025
so keep that thing in the heap  
as long as this is around,      

1519
01:18:19,094 --> 01:18:20,794
because I need it,              
I'm pointing to it.             

1520
01:18:20,863 --> 01:18:21,795
That's the default.             

1521
01:18:21,864 --> 01:18:24,431
So, we never actually           
type the keyword strong.        

1522
01:18:24,500 --> 01:18:25,666
It's the default.               
It's always there.              

1523
01:18:25,735 --> 01:18:27,501
It's kind of like internal      
with that access control.       

1524
01:18:27,569 --> 01:18:29,736
We don't actually               
ever type that.                 

1525
01:18:29,805 --> 01:18:33,340
Now weak, you've actually seen  
before. You all remember weak?  

1526
01:18:33,409 --> 01:18:35,109
It was on the outlets. Okay,    

1527
01:18:35,178 --> 01:18:37,510
when we made that outlet        
connection, I said oh,          

1528
01:18:37,579 --> 01:18:40,214
that, see that weak? I'm gonna  
tell you about that next week.  

1529
01:18:40,282 --> 01:18:43,017
Well, I'm living up to my       
promise, I'm telling you about  

1530
01:18:43,086 --> 01:18:47,121
weak. What does weak mean?      
Weak means I'm                  

1531
01:18:47,189 --> 01:18:50,690
pointing to this thing in       
the heap, but I'm only really   

1532
01:18:50,759 --> 01:18:54,628
interested in it if someone     
else is interested in it.       

1533
01:18:54,697 --> 01:18:57,697
In other words, if someone      
else has a strong pointer to    

1534
01:18:57,766 --> 01:19:00,534
it, keep it in the heap.        
But as soon as no one else is   

1535
01:19:00,603 --> 01:19:01,802
interested in this,             
in other words,                 

1536
01:19:01,871 --> 01:19:05,505
all other strong pointers       
go away. Set me to nil and      

1537
01:19:05,574 --> 01:19:10,243
throw the thing out of          
the heap. So this is the don't  

1538
01:19:10,312 --> 01:19:14,414
keep that thing in the heap on  
my account kind of pointer.     

1539
01:19:14,483 --> 01:19:17,384
And notice that it gets set to  
nil if all the other strong     

1540
01:19:17,453 --> 01:19:20,253
pointers go away. So what kind  
of type does this have to be?   

1541
01:19:20,322 --> 01:19:23,457
It has to be an optional.       

1542
01:19:23,525 --> 01:19:28,362
So this weak only works         
with optional pointers to       

1543
01:19:28,430 --> 01:19:31,966
reference types, okay,          
things that are in the heap,    

1544
01:19:32,034 --> 01:19:34,901
which our outlets are.          
If you remember our outlets,    

1545
01:19:34,970 --> 01:19:38,839
like flip count label was a UI  
label exclamation point. That   

1546
01:19:38,908 --> 01:19:41,875
was an implicitly unwrapped     
optional. It was an optional,   

1547
01:19:41,944 --> 01:19:44,945
right? Same thing card buttons  
was an implicitly unwrapped     

1548
01:19:45,014 --> 01:19:49,817
optional. So those pointers     
to things in the UI.            

1549
01:19:49,885 --> 01:19:52,619
If for some reason those        
things left the UI, okay,       

1550
01:19:52,688 --> 01:19:55,589
got removed from the UI         
somehow, which is possible,     

1551
01:19:55,657 --> 01:19:59,660
but rare. Then those things     
would get set to nil, okay?     

1552
01:19:59,728 --> 01:20:00,994
And you would no longer         
be pointing to them,            

1553
01:20:01,063 --> 01:20:01,828
and that's what they want.      

1554
01:20:01,897 --> 01:20:04,130
Because if there's              
no flip count label,            

1555
01:20:04,199 --> 01:20:07,234
there's no use trying           
to update it. So                

1556
01:20:07,303 --> 01:20:10,170
that's why they make those      
weak All right, now, weak,      

1557
01:20:10,239 --> 01:20:12,772
there's only a couple of        
places that we use we           

1558
01:20:12,841 --> 01:20:15,842
commonly. One is for outlets,   
another one is for delegation.  

1559
01:20:15,911 --> 01:20:19,246
Remember back to my NBC talk,   
I talked about the delegation,  

1560
01:20:19,314 --> 01:20:21,815
the data source. And we have    
these pointers from the view    

1561
01:20:21,883 --> 01:20:23,950
back to the controller where    
there's that blind and          

1562
01:20:24,019 --> 01:20:25,552
structure of                    
communication all that,         

1563
01:20:25,621 --> 01:20:27,320
which I'm gonna talk            
about on Wednesday.             

1564
01:20:27,389 --> 01:20:30,090
Those pointers are weak,        
because the view,               

1565
01:20:30,159 --> 01:20:32,959
if the thing that they're       
sending will did and            

1566
01:20:33,028 --> 01:20:36,563
should to goes away, well,      
they're not gonna send those    

1567
01:20:36,632 --> 01:20:40,400
messages anymore, so they want  
to be nil, okay. There's no     

1568
01:20:40,469 --> 01:20:43,970
one to send their messages to   
then they just want to be nil,  

1569
01:20:44,039 --> 01:20:45,872
okay. They don't want to        
be pointed to something.        

1570
01:20:45,941 --> 01:20:48,475
They certainly don't want       
a thing it points to,           

1571
01:20:48,544 --> 01:20:50,543
to get stuck in                 
the heap because of it.         

1572
01:20:50,612 --> 01:20:53,179
Because they're happy to just   
not send the messages if        

1573
01:20:53,248 --> 01:20:55,882
that thing wants to leave       
the heap, otherwise we don't    

1574
01:20:55,951 --> 01:21:00,754
use weak that much.             
Okay, last is unowned.          

1575
01:21:00,823 --> 01:21:03,223
Unowned is don't                
reference count this,           

1576
01:21:03,292 --> 01:21:06,659
in other words I'm pointing     
to something in the heap, but   

1577
01:21:06,728 --> 01:21:10,163
don't count it as a strong      
pointer. And I promise I'll     

1578
01:21:10,232 --> 01:21:14,668
never access this thing when    
it's gone from the heap. Now,   

1579
01:21:14,737 --> 01:21:17,537
this is very dangerous,         
this is basically trying to     

1580
01:21:17,606 --> 01:21:20,474
outsmart the automatic          
reference counting system.      

1581
01:21:20,542 --> 01:21:23,877
You're saying, you know when    
it's in the heap or not, and    

1582
01:21:23,946 --> 01:21:26,113
this is really rare.            
And the way,                    

1583
01:21:26,182 --> 01:21:30,584
the one time we use this is to  
avoid a memory cycle, okay.     

1584
01:21:30,653 --> 01:21:32,052
Everyone know what              
a memory cycle is,              

1585
01:21:32,121 --> 01:21:33,854
that's where you have           
something in the heap and       

1586
01:21:33,922 --> 01:21:35,522
it points to something          
else in the heap, and           

1587
01:21:35,591 --> 01:21:36,657
that thing points back to it.   

1588
01:21:36,725 --> 01:21:39,159
So, they're pointing to each    
other, keeping each other in    

1589
01:21:39,228 --> 01:21:41,728
the heap. But no one else is    
interested in them. No one      

1590
01:21:41,797 --> 01:21:44,465
points to either of them. They  
only just point to each other.  

1591
01:21:44,533 --> 01:21:46,533
So they're just sitting in      
the heap for no reason.         

1592
01:21:46,601 --> 01:21:49,769
No one's even accessing them,   
that's a memory cycle. And      

1593
01:21:49,838 --> 01:21:53,540
memory cycles aren't generally  
created in Swift normally but   

1594
01:21:53,609 --> 01:21:56,443
there's one way they're         
easy to create which is         

1595
01:21:56,511 --> 01:21:57,577
closures, okay.                 

1596
01:21:57,646 --> 01:22:00,113
Which is a feature I'm gonna    
talk about on Wednesday, okay.  

1597
01:22:00,182 --> 01:22:05,285
And so we will use unowned      
with closures. All right,       

1598
01:22:05,353 --> 01:22:07,821
back to our list of data        
structures here, of course      

1599
01:22:07,889 --> 01:22:10,590
there's struct we know all      
about that. It's a value type,  

1600
01:22:10,659 --> 01:22:12,893
it's copy owned right, there's  
no inheritance of data.         

1601
01:22:12,962 --> 01:22:15,495
But you're gonna learn with     
protocols there is inheritance  

1602
01:22:15,564 --> 01:22:16,330
of functionality,               

1603
01:22:16,398 --> 01:22:19,432
in fact multiple inheritance    
of functionality. And you've    

1604
01:22:19,501 --> 01:22:24,905
seen examples of struct cards,  
dictionary, string, character,  

1605
01:22:24,973 --> 01:22:29,476
int, double, UInt32,            
lots of structs have happened   

1606
01:22:29,545 --> 01:22:32,378
there. And I have here, let's   
jump over to concentrations     

1607
01:22:32,447 --> 01:22:35,315
see what happens when we make   
concentration of struct.        

1608
01:22:35,384 --> 01:22:37,017
I start off the next one with   
that because we're pretty much  

1609
01:22:37,018 --> 01:22:38,651
How about                       

1610
01:22:38,721 --> 01:22:41,121
out of time here.               
Enum, I'm not going to,         

1611
01:22:41,189 --> 01:22:44,624
oh yes, this is the demo,       
which I will do next time. And  

1612
01:22:44,693 --> 01:22:47,794
then enum here we already just  
covered, so I'm not going to    

1613
01:22:47,863 --> 01:22:51,497
talk about it, another value    
type, discrete values. It also  

1614
01:22:51,566 --> 01:22:55,702
can have inherit the same kind  
of functionality inheritance.   

1615
01:22:55,771 --> 01:22:59,172
This functionality inheritance  
that I keep kind of mentioning  

1616
01:22:59,241 --> 01:23:02,342
is done using this last one,    
which is called protocols.      

1617
01:23:02,411 --> 01:23:04,845
So I'm gonna start off on       
Wednesday with a detailed       

1618
01:23:04,913 --> 01:23:06,613
explanation of what             
a protocol is.                  

1619
01:23:06,682 --> 01:23:10,016
It's fundamental to the design  
of all of foundation,           

1620
01:23:10,085 --> 01:23:12,819
all the array,                  
dictionary, string, int.        

1621
01:23:12,888 --> 01:23:15,522
And all of those things         
fundamentally using protocols   

1622
01:23:15,591 --> 01:23:17,758
everywhere, massive             
number of protocols.            

1623
01:23:17,826 --> 01:23:20,093
And it's also fundamental with  
things like delegation and      

1624
01:23:20,162 --> 01:23:22,796
stuff like that, so it's very,  
very important. And to round    

1625
01:23:22,865 --> 01:23:26,332
out our full understanding of   
how to build data structures    

1626
01:23:26,401 --> 01:23:30,436
in Swift. Okay, so we'll start  
off on Wednesday with that and  

1627
01:23:30,505 --> 01:23:32,739
I will see you then.            
>> For more,                    

1628
01:23:32,808 --> 01:23:41,314
please visit us                 
at stanford.edu.                
