Addes default __eq__() to BindingSpec, so that DAG binding spec depen…

…dencies can have equal but not identical dependencies.

README.rst

@@ -370,6 +370,30 @@ binding spec A can be a dependency of B and of C, and binding spec D can have
 dependencies on B and C.  Even though there are multiple dependency paths from
 D to A, the bindings in binding spec A will only be evaluated once.
 
+The binding spec instance of A that is a dependency of B is considered the
+same as the instance that is a dependency of C if the two instances are equal
+(via ``__eq__()``).  The default implementation of ``__eq__()`` in
+``BindingSpec`` says that two binding specs are equal if they are of exactly
+the same python type.  You will need to override ``__eq__()`` (as well as
+``__hash__()``) if your binding spec is parameterized, i.e., if it takes one
+or more initializer args so that two instances of the binding spec may behave
+differently.
+
+.. code-block:: python
+
+    >>> class SomeBindingSpec(pinject.BindingSpec):
+    ...     def __init__(self, the_instance):
+    ...         self._the_instance = the_instance
+    ...     def configure(self, bind):
+    ...         bind('foo', to_instance=self._the_instance)
+    ...     def __eq__(self, other):
+    ...         return (type(self) == type(other) and
+    ...                 self._the_instance == other._the_instance)
+    ...     def __hash__(self):
+    ...         return hash(type(self)) ^ hash(self._the_instance)
+    ...
+    >>>
+
 Provider methods
 ----------------
 
@@ -1218,6 +1242,7 @@ Changelog
 
 v0.10:
 
+* Added default ``__eq__()`` to ``BindingSpec``, so that DAG binding spec dependencies can have equal but not identical dependencies.
 * Allowed customizing ``configure()`` and ``dependencies()`` binding spec method names.
 * Deprecated ``@injectable`` in favor of ``@inject``.
 * Added partial injection.

pinject/bindings.py

@@ -293,6 +293,12 @@ def configure(self, bind):
     def dependencies(self):
         return []
 
+    def __eq__(self, other):
+        return type(self) == type(other)
+
+    def __hash__(self):
+        return hash(type(self))
+
 
 def get_provider_fn_bindings(provider_fn, default_arg_names):
     provider_decorations = decorators.get_provider_fn_decorations(

pinject/bindings_test.py

@@ -408,6 +408,33 @@ def test_binding_to_non_class_raises_error(self):
                           to_class='not-a-class')
 
 
+class BindingSpecTest(unittest.TestCase):
+
+    def test_equal_if_same_type(self):
+        class SomeBindingSpec(bindings_lib.BindingSpec):
+            pass
+        self.assertEqual(SomeBindingSpec(), SomeBindingSpec())
+
+    def test_not_equal_if_not_same_type(self):
+        class BindingSpecOne(bindings_lib.BindingSpec):
+            pass
+        class BindingSpecTwo(bindings_lib.BindingSpec):
+            pass
+        self.assertNotEqual(BindingSpecOne(), BindingSpecTwo())
+
+    def test_hash_equal_if_same_type(self):
+        class SomeBindingSpec(bindings_lib.BindingSpec):
+            pass
+        self.assertEqual(hash(SomeBindingSpec()), hash(SomeBindingSpec()))
+
+    def test_hash_not_equal_if_not_same_type(self):
+        class BindingSpecOne(bindings_lib.BindingSpec):
+            pass
+        class BindingSpecTwo(bindings_lib.BindingSpec):
+            pass
+        self.assertNotEqual(hash(BindingSpecOne()), hash(BindingSpecTwo()))
+
+
 class GetProviderFnBindingsTest(unittest.TestCase):
 
     def test_proviser_calls_provider_fn(self):

pinject/object_graph_test.py

@@ -78,13 +78,12 @@ def test_allows_dag_binding_spec_dependencies(self):
         class CommonBindingSpec(bindings.BindingSpec):
             def configure(self, bind):
                 bind('foo', to_instance='a-foo')
-        a_common_binding_spec = CommonBindingSpec()
         class BindingSpecOne(bindings.BindingSpec):
             def dependencies(self):
-                return [a_common_binding_spec]
+                return [CommonBindingSpec()]
         class BindingSpecTwo(bindings.BindingSpec):
             def dependencies(self):
-                return [a_common_binding_spec]
+                return [CommonBindingSpec()]
         class RootBindingSpec(bindings.BindingSpec):
             def dependencies(self):
                 return [BindingSpecOne(), BindingSpecTwo()]