Function collections (#156)

* Add FunctionCollection as a type

* wip

* 'Refactored by Sourcery' (#157)

Co-authored-by: Sourcery AI <>

* wip

* wip

* tested definitions for function collections

* changelog update

* removed the magic. I didn't like it

* fix some merge mess up in the changelog

Co-authored-by: sourcery-ai[bot] <58596630+sourcery-ai[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Enhancements
 * container.partial now works for instance methods. Thanks to @LeafyLappa for pointing out this didn't work.
+* Added FunctionCollection type. Allows the container to store a collection of functions
 
 ### Bug Fixes
 * container.partial now works for instance methods. Thanks to @LeafyLappa for pointing out this didn't work.

lagom/__init__.py

@@ -1,14 +1,15 @@
 """Lagom, a type based dependency injection container"""
-from .version import __version__
-from .debug import get_build_info
-from .definitions import Singleton, Alias, UnresolvableTypeDefinition
 from .container import Container, ExplicitContainer
+from .debug import get_build_info
 from .decorators import (
     bind_to_container,
     magic_bind_to_container,
     dependency_definition,
 )
+from .definitions import Singleton, Alias, UnresolvableTypeDefinition
 from .markers import injectable
+from .util.functional import FunctionCollection
+from .version import __version__
 
 __all__ = [
     "__version__",
@@ -18,6 +19,7 @@
     "UnresolvableTypeDefinition",
     "Container",
     "ExplicitContainer",
+    "FunctionCollection",
     "bind_to_container",
     "magic_bind_to_container",
     "dependency_definition",

lagom/definitions.py

@@ -149,9 +149,9 @@ def normalise(
     if isinstance(resolver, SpecialDepDefinition):
         return resolver
     elif inspect.isfunction(resolver):
-        return construction(resolver)
+        return construction(resolver)  # type: ignore
     elif inspect.iscoroutinefunction(resolver):
-        return construction(resolver)
+        return construction(resolver)  # type: ignore
     elif inspect.isclass(resolver):
         return Alias(resolver, skip_alias_definitions)
     else:

lagom/util/functional.py

@@ -1,7 +1,7 @@
 """Code to help understand functions
 """
 import inspect
-from typing import Callable
+from typing import Callable, TypeVar, Generic, Iterator
 
 
 def arity(func: Callable) -> int:
@@ -16,3 +16,35 @@ def arity(func: Callable) -> int:
     :return:
     """
     return len(inspect.signature(func).parameters)
+
+
+F = TypeVar("F", bound=Callable)
+
+
+class FunctionCollection(Generic[F]):
+    """
+    Represents a collection of functions that is hashable.
+    """
+
+    def __init__(self, *checkers: F):
+        self._checkers = checkers
+        self.hash = hash(tuple(self._checkers))
+
+    def __len__(self) -> int:
+        return len(self._checkers)
+
+    def __contains__(self, item) -> bool:
+        return item in self._checkers
+
+    def __iter__(self) -> Iterator[F]:
+        return iter(self._checkers)
+
+    def __hash__(self):
+        return self.hash
+
+    def __eq__(self, other):
+        if isinstance(other, FunctionCollection):
+            return self.hash == other.hash
+        if isinstance(other, list):
+            return tuple(other) == self._checkers
+        return False

tests/test_function_collections.py

@@ -0,0 +1,21 @@
+from typing import Callable
+
+from lagom import Container, FunctionCollection
+
+
+def _func_a(input: str) -> str:
+    return f"func_a({input})"
+
+
+def _func_b(input: str) -> str:
+    return f"func_b({input})"
+
+
+SomeSignature = Callable[[str], str]
+
+
+def test_a_function_collection_can_be_used_by_a_container(
+    container: Container,
+):
+    container[FunctionCollection[SomeSignature]] = FunctionCollection(_func_a, _func_b)
+    assert container[FunctionCollection[SomeSignature]] == [_func_a, _func_b]

tests/util/test_functional.py

@@ -1,6 +1,14 @@
 import pytest
 
-from lagom.util.functional import arity
+from lagom.util.functional import arity, FunctionCollection
+
+
+def _func_a():
+    pass
+
+
+def _func_b():
+    pass
 
 
 @pytest.mark.parametrize(
@@ -9,3 +17,16 @@
 )
 def test_we_can_get_arity_from_functions(test_func, expected_arity: int):
     assert arity(test_func) == expected_arity
+
+
+def test_function_collections_are_the_same_if_they_have_the_same_functions():
+    assert FunctionCollection(_func_a, _func_b) == FunctionCollection(_func_a, _func_b)
+
+
+def test_function_collections_have_equality_to_a_list_of_those_functions():
+    assert FunctionCollection(_func_a, _func_b) == [_func_a, _func_b]
+
+
+def test_function_collections_are_iterable():
+    collected_funcs = [func for func in FunctionCollection(_func_a, _func_b)]
+    assert collected_funcs == [_func_a, _func_b]