Methods in Ruby

Overview

In this lesson, we'll introduce methods, distinguish them from data types, and cover how to create and execute them in your Ruby program.

You can follow along using IRB by typing irb in your terminal and copying the provided code examples. Alternatively, in the lib folder, there is also a file, example.rb, that you can use to copy the code examples into. You can run this file from the lesson's main directory by typing ruby lib/example.rb to see what it produces.

Objectives

• Describe how methods can define new routines and procedures for our code.
• Define a method with the def keyword, supply the method's body, and close the method definition with the end keyword.
• Invoke a method by calling it by name.

Video

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Introduction to Ruby Methods

Why Use Methods

Methods define a new thing that your program can do. Variables are a mechanism to teach your Ruby program about data; methods teach your Ruby program about a new routine or behavior it can use. Variables are like nouns, methods are like verbs.

For example, imagine needing to say "Hello World!" ten times. You might do something like this:

phrase = "Hello World!"
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase

That works pretty well. You made use of a variable to encapsulate the data you wanted to print and then the next ten lines literally print the phrase.

Now imagine later in your program you again want to say "Hello World!" ten times. The entire program would look something like this:

phrase = "Hello World!"
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase

# ... The rest of the program

puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase
puts phrase

We have to repeat the literal procedure for printing the value of phrase ten times. If variables encapsulate and abstract data, methods encapsulate and abstract procedure. Instead of literally puts phrase ten times, we can instead build a method—a little machine that does exactly that whenever we want.

The method would look like this:

def say_hello_world_ten_times
  phrase = "Hello World!"
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
end

Now, when we use the bareword say_hello_world_ten_times in our program, it will invoke the method, running the code within the method. So the script above, saying hello ten times, doing other things, then saying hello ten times again could be rewritten as this:

def say_hello_world_ten_times
  phrase = "Hello World!"
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
  puts phrase
end

say_hello_world_ten_times

# ... The rest of the program

say_hello_world_ten_times

That's way cleaner and follows the code principle "Don't Repeat Yourself" or DRY. We abstract the action or procedure of putting "Hello World!" ten times into a method. By defining the method say_hello_world_ten_times once, we can "call" or "invoke" the method as many times as we want in the future. Let's look at methods in greater detail.

Defining a Method

You can define a method in Ruby with the def keyword. A method's name can begin with any lowercase letter. Here's a quick example:

def greeting # Method Signature
  puts "Hello World" # Method Body
end # Method Closing

Note: In the snippet above, we are using the # in a different way than we've seen before. Here we are using it to put comments inside our code. Ruby will see the # in the line of code (without the rest of the syntax required for string interpolation) and will not interpret anything that follows. You can use # in this way to add comments or clarifications to your code, either at the end of a line of code as shown above or on a line by themselves. You can also use it to "comment out" code (by putting # at the beginning of each line) if you want to keep the code from executing temporarily. This can come in handy during debugging.

The first line in the code snippet above, def greeting, is called the method signature, it defines the basic properties of the method including the name of the method, greeting.

Once you 'open' a method definition with the def keyword, all subsequent lines in your program are considered the method's body, the actual procedure or code that your method will run every time it's called.

You must terminate every opening def of a method with a corresponding end in order to close the method body. If you don't correctly end a method, your program will have unexpected results or break entirely because of a syntax error. A good practice is to define the method and then immediately close it before programming anything into the method.

def greeting
  # Leave a line break for the method body
end # Immediately close the method.

Here we set up the method's structure first, ensuring a proper termination before adding any other complexity.

Aside: It's also a great practice to indent methods correctly. The body of a method should be indented two (2) spaces, placing it visually within the method. When you end the method, go back to the same indentation of the def, aligning the opening and closing of the method visually. Then you can easily define the body of the method and never worry about forgetting to end the method.

def greeting
  puts "Hello World" # Now code the body of the method.
end

Invoking a Method

Once you define a method, you can execute the method whenever you want by using the method name in your code.

def greeting
  puts "Hello World"
end

greeting # Executing the method by name
#=> "Hello World"

greeting # Executing the method again
#=> "Hello World"

Note: If you have been using IRB so far, exit out of it before continuing. The remaining portion of this lesson involves bash commands you will need to enter into the terminal.

Let's try making a method we can use over and over. Make a new file called greeting.rb (you can use: touch greeting.rb from your terminal). Put the following code in it:

File: greeting.rb

def greeting
  puts "Hello World"
end

Save your file and run it with ruby greeting.rb. You'll see:

$ ruby greeting.rb
$

You'll notice that when you run your program, nothing happens. Your program successfully defined the method but it never executed it. Just because you built a machine doesn't mean that you turned it on. Update your greeting.rb to entirely read:

File: greeting.rb

def greeting
  puts "Hello World"
end

greeting

Save your file and run it with ruby greeting.rb. You'll see:

$ ruby greeting.rb
Hello World
$

Now your program actually executed the program. Update the code again to entirely read:

File: greeting.rb

def greeting
  puts "Hello World"
end

greeting
greeting
greeting
greeting
greeting

Save your file and run it with ruby greeting.rb. You'll see:

$ ruby greeting.rb
Hello World
Hello World
Hello World
Hello World
Hello World
$

The bareword greeting will execute the body of the defined method.

Writing Code vs Reading About Code

Let's end by talking briefly about one additional use of #. Programmers love conventions, or agreed upon rules that help them talk to each other about code. A common syntax convention for Ruby methods is to preface them with a #, and in subsequent lessons, you might see method names written with a # in front of them. For example, if a method is named 'greeting', rubyists will often refer to it as #greeting. This is so that other rubyists can instantly recognize it as a method, as opposed to a variable or a bareword or a class. But remember that when you write it in your code, it should be greeting and not #greeting.