Merge pull request #5 from cbefus/abc

Rework to use an abstract base class.

README.md

@@ -82,25 +82,7 @@ So we present you with an **Optional** object as an alternative.
     print(thing)
     ```
 
-6. But you **can't** get the value without first checking for presence:
-    ```python
-    thing = some_func_returning_an_optional()
-    print(thing.get()) # **will raise an exception**
-
-    ```
-    but:
-    ```python
-    thing = some_func_returning_an_optional()
-    if thing.is_present(): # could use is_empty() as alternative
-        print(thing.get()) # **does not throw**
-    ```
-    instead of:
-    ```python
-    if thing is not None:
-        print(thing)
-    ```
-
-7. You **can't** get the value if its empty:
+6. You **can't** get the value if its empty:
     ```python
     thing = some_func_returning_an_optional()
     if thing.is_empty():
@@ -112,7 +94,7 @@ So we present you with an **Optional** object as an alternative.
         print(None) # very odd
     ```
 
-8. **__Best Usage:__** You can chain on presence:
+7. **__Best Usage:__** You can chain on presence:
     ```python
     thing = some_func_returning_an_optional()
     thing.if_present(lambda thing: print(thing))
@@ -123,7 +105,7 @@ So we present you with an **Optional** object as an alternative.
         print(thing)
     ```
 
-9. **__Best Usage:__** You can chain on non presence:
+8. **__Best Usage:__** You can chain on non presence:
     ```python
     thing = some_func_returning_an_optional()
     thing.if_present(lambda thing: print(thing)).or_else(lambda _: print("PANTS!"))
@@ -136,45 +118,33 @@ So we present you with an **Optional** object as an alternative.
         print("PANTS!")
     ```
 
-10. **__Best Usage:__** You can map a function:
+9. **__Best Usage:__** You can map a function:
     ```python
     def mapping_func(thing):
         return thing + "PANTS"
-    
+
     thing_to_map = Optional.of("thing")
     mapped_thing = thing_to_map.map(mapping_func) # returns Optional.of("thingPANTS")
     ```
     Note that if the mapping function returns `None` then the map call will return `Optional.empty()`. Also
     if you call `map` on an empty optional it will return `Optional.empty()`.
-    
-11. **__Best Usage:__** You can flat map a function which returns an Optional.
+
+10. **__Best Usage:__** You can flat map a function which returns an Optional.
     ```python
     def flat_mapping_func(thing):
         return Optional.of(thing + "PANTS")
-    
+
     thing_to_map = Optional.of("thing")
     mapped_thing = thing_to_map.map(mapping_func) # returns Optional.of("thingPANTS")
     ```
-    Note that this does not return an Optional of an Optional.  __Use this for mapping functions which return optionals.__ 
+    Note that this does not return an Optional of an Optional.  __Use this for mapping functions which return optionals.__
     If the mapping function you use with this does not return an Optional, calling `flat_map` will raise a
     `FlatMapFunctionDoesNotReturnOptionalException`.
 
-12. You can compare two optionals:
+11. You can compare two optionals:
     ```python
     Optional.empty() == Optional.empty() # True
     Optional.of("thing") == Optional.of("thing") # True
     Optional.of("thing") == Optional.empty() # False
     Optional.of("thing") == Optional.of("PANTS") # False
     ```
-
-
-
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-
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-
-

optional/__init__.py

@@ -0,0 +1 @@
+from .optional import *

optional/compatible_abc.py

@@ -0,0 +1,12 @@
+"""compatible_abc
+
+This module exports a single class, CompatibleABC.
+It is necessary to provide the same behavior in
+Python 2 and Python 3.
+
+The implementation was taken from https://stackoverflow.com/a/38668373
+"""
+from abc import ABCMeta
+
+
+CompatibleABC = ABCMeta('ABC', (object,), {'__slots__': ()})

optional/optional.py

@@ -0,0 +1,109 @@
+from abc import abstractmethod
+
+from .compatible_abc import CompatibleABC
+
+
+class Optional(object):
+    @staticmethod
+    def of(thing):
+        return _Nothing() if thing is None else _Something(thing)
+
+    @staticmethod
+    def empty():
+        return _Nothing()
+
+
+class _AbstractOptional(CompatibleABC):
+
+    @abstractmethod
+    def is_present(self):
+        pass
+
+    def is_empty(self):
+        return not self.is_present()
+
+    @abstractmethod
+    def get(self):
+        pass
+
+    @abstractmethod
+    def if_present(self, consumer):
+        pass
+
+    @abstractmethod
+    def or_else(self, procedure):
+        pass
+
+    @abstractmethod
+    def map(self, func):
+        pass
+
+    @abstractmethod
+    def flat_map(self, func):
+        pass
+
+
+class _Nothing(_AbstractOptional):
+    def is_present(self):
+        return False
+
+    def get(self):
+        raise OptionalAccessOfEmptyException(
+            "You cannot call get on an empty optional"
+        )
+
+    def if_present(self, consumer):
+        return self
+
+    def or_else(self, procedure):
+        return procedure()
+
+    def map(self, func):
+        return self
+
+    def flat_map(self, func):
+        return self
+
+    def __eq__(self, other):
+        return isinstance(other, _Nothing)
+
+
+class _Something(_AbstractOptional):
+    def __init__(self, value):
+        self.__value = value
+
+    def is_present(self):
+        return True
+
+    def get(self):
+        return self.__value
+
+    def if_present(self, consumer):
+        consumer(self.get())
+        return self
+
+    def or_else(self, procedure):
+        return self
+
+    def map(self, func):
+        return Optional.of(func(self.get()))
+
+    def flat_map(self, func):
+        res = func(self.get())
+        if not isinstance(res, _AbstractOptional):
+            raise FlatMapFunctionDoesNotReturnOptionalException(
+                "Mapping function to flat_map must return Optional."
+            )
+
+        return res
+
+    def __eq__(self, other):
+        return isinstance(other, _Something) and self.get() == other.get()
+
+
+class OptionalAccessOfEmptyException(Exception):
+    pass
+
+
+class FlatMapFunctionDoesNotReturnOptionalException(Exception):
+    pass

test_optional.py → test/test_optional.py

@@ -1,12 +1,16 @@
 import unittest
 
-from optional import Optional, OptionalAccessWithoutCheckingPresenceException, OptionalAccessOfEmptyException, FlatMapFunctionDoesNotReturnOptionalException
+from optional import (
+    Optional,
+    OptionalAccessOfEmptyException,
+    FlatMapFunctionDoesNotReturnOptionalException
+)
 
 
 class TestOptional(unittest.TestCase):
 
     def test_can_instantiate(self):
-        Optional(None)
+        Optional.of(None)
 
     def test_instantiate_empty(self):
         optional = Optional.empty()
@@ -28,11 +32,6 @@ def test_is_not_present_with_empty(self):
         optional = Optional.of(None)
         self.assertFalse(optional.is_present())
 
-    def test_cannot_get_without_checking_presence(self):
-        optional = Optional.of("thing")
-        with self.assertRaises(OptionalAccessWithoutCheckingPresenceException):
-            optional.get()
-
     def test_cannot_get_from_empty_even_after_checking(self):
         optional = Optional.empty()
         self.assertTrue(optional.is_empty())
@@ -156,7 +155,3 @@ def test_non_empty_optionals_with_non_equal_content_are_not_equal(self):
 
     def test_non_empty_optionals_with_equal_content_are_equal(self):
         self.assertEqual(Optional.of("PANTS"), Optional.of("PANTS"))
-
-
-if __name__ == '__main__':
-    unittest.main()