Commmon: Add register_convention()

monkey/common/di_container.py

@@ -21,6 +21,7 @@ class DIContainer:
     def __init__(self):
         self._type_registry = {}
         self._instance_registry = {}
+        self._convention_registry = {}
 
     def register(self, interface: Type[T], concrete_type: Type[T]):
         """
@@ -60,6 +61,34 @@ class DIContainer:
         self._instance_registry[interface] = instance
         DIContainer._del_key(self._type_registry, interface)
 
+    def register_convention(self, type_: Type[T], name: str, instance: T):
+        """
+        Register an instance as a convention
+
+        At times — particularly when dealing with primative types — it can be useful to define a
+        convention for how dependencies should be resolved. For example, you might want any class
+        that specifies `hostname: str` in its constructor to receive the hostname of the system it's
+        running on. Registering a convention allows you to assign an object instance to a type, name
+        pair.
+
+        Example:
+            class TestClass:
+                def __init__(self, hostname: str):
+                    self.hostname = hostname
+
+            di_container = DIContainer()
+            di_container.register_convention(str, "hostname", "my_hostname.domain")
+
+            test = di_container.resolve(TestClass)
+            assert test.hostname == "my_hostname.domain"
+
+        :param **type_**: The `type` (class) of the dependency
+        :param name: The name of the dependency parameter
+        :param instance: An instance (object) of `type_` that will be injected into constructors
+                         that specify `[name]: [type_]` as parameters
+        """
+        self._convention_registry[(type_, name)] = instance
+
     def resolve(self, type_: Type[T]) -> T:
         """
         Resolves all dependencies and returns a new instance of `type_` using constructor dependency
@@ -88,12 +117,25 @@ class DIContainer:
         """
         args = []
 
-        for arg_type in inspect.getfullargspec(type_).annotations.values():
-            instance = self._resolve_type(arg_type)
+        for arg_name, arg_type in inspect.getfullargspec(type_).annotations.items():
+            try:
+                instance = self._resolve_convention(arg_type, arg_name)
+            except UnregisteredConventionError:
+                instance = self._resolve_type(arg_type)
+
             args.append(instance)
 
         return tuple(args)
 
+    def _resolve_convention(self, type_: Type[T], name: str) -> T:
+        convention_identifier = (type_, name)
+        try:
+            return self._convention_registry[convention_identifier]
+        except KeyError:
+            raise UnregisteredConventionError(
+                f"Failed to resolve unregistered convention {convention_identifier}"
+            )
+
     def _resolve_type(self, type_: Type[T]) -> T:
         if type_ in self._type_registry:
             return self._construct_new_instance(type_)

monkey/tests/unit_tests/common/test_di_container.py

@@ -281,3 +281,88 @@ def test_register_instance_with_conflicting_type(container):
     service_b_instance = ServiceB()
     with pytest.raises(TypeError):
         container.register_instance(IServiceA, service_b_instance)
+
+
+class TestClass6:
+    __test__ = False
+
+    def __init__(self, my_str: str):
+        self.my_str = my_str
+
+
+def test_register_convention(container):
+    my_str = "test_string"
+    container.register_convention(str, "my_str", my_str)
+
+    test_6 = container.resolve(TestClass6)
+
+    assert test_6.my_str == my_str
+
+
+class TestClass7:
+    __test__ = False
+
+    def __init__(self, my_str1: str, my_str2: str):
+        self.my_str1 = my_str1
+        self.my_str2 = my_str2
+
+
+def test_register_convention__multiple_parameters_same_type(container):
+    my_str1 = "s1"
+    my_str2 = "s2"
+    container.register_convention(str, "my_str2", my_str2)
+    container.register_convention(str, "my_str1", my_str1)
+
+    test_7 = container.resolve(TestClass7)
+    assert test_7.my_str1 == my_str1
+    assert test_7.my_str2 == my_str2
+
+
+class TestClass8:
+    __test__ = False
+
+    def __init__(self, my_str: str, my_int: int):
+        self.my_str = my_str
+        self.my_int = my_int
+
+
+def test_register_convention__multiple_parameters_different_types(container):
+    my_str = "test_string"
+    my_int = 42
+    container.register_convention(str, "my_str", my_str)
+    container.register_convention(int, "my_int", my_int)
+
+    test_8 = container.resolve(TestClass8)
+    assert test_8.my_str == my_str
+    assert test_8.my_int == my_int
+
+
+class TestClass9:
+    __test__ = False
+
+    def __init__(self, service_a: IServiceA, my_str: str):
+        self.service_a = service_a
+        self.my_str = my_str
+
+
+def test_register_convention__type_properly_resolved(container):
+    my_str = "test_string"
+
+    container.register(IServiceA, ServiceA)
+    container.register_convention(str, "my_str", my_str)
+    test_9 = container.resolve(TestClass9)
+
+    assert isinstance(test_9.service_a, ServiceA)
+    assert test_9.my_str == my_str
+
+
+def test_register_convention__instance_properly_resolved(container):
+    service_a_instance = ServiceA()
+    my_str = "test_string"
+
+    container.register_instance(IServiceA, service_a_instance)
+    container.register_convention(str, "my_str", my_str)
+    test_9 = container.resolve(TestClass9)
+
+    assert id(service_a_instance) == id(test_9.service_a)
+    assert test_9.my_str == my_str