Wiring by string id (#403)

* Add prototype implementation

* Implement wiring by string id

* Fix pydocstyle errors

* Refactor wiring module

* Fix flake8 errors

* Update changelog

* Fix flake8 errors

* Add example and docs

Author: rmk135

docs/main/changelog.rst

@@ -9,6 +9,7 @@ follows `Semantic versioning`_
 
 Development version
 -------------------
+- Add wiring by string id.
 - Improve error message for ``Dependency`` provider missing attribute.
 
 4.25.1

docs/wiring.rst

@@ -88,6 +88,82 @@ Also you can use ``Provide`` marker to inject a container.
    :emphasize-lines: 16-19
    :lines: 3-
 
+Strings identifiers
+-------------------
+
+You can use wiring with string identifiers. String identifier should match provider name in the container:
+
+.. literalinclude:: ../examples/wiring/example_string_id.py
+   :language: python
+   :emphasize-lines: 17
+   :lines: 3-
+
+With string identifiers you don't need to use a container to specify an injection.
+
+To specify an injection from a nested container use point ``.`` as a separator:
+
+.. code-block:: python
+
+   @inject
+   def foo(service: UserService = Provide['services.user']) -> None:
+       ...
+
+You can also use injection modifiers:
+
+.. code-block:: python
+
+   from dependency_injector.wiring import (
+       inject,
+       Provide,
+       as_int,
+       as_float,
+       as_,
+       required,
+       invariant,
+       provided,
+   )
+
+
+   @inject
+   def foo(value: int = Provide['config.option', as_int()]) -> None:
+       ...
+
+
+   @inject
+   def foo(value: float = Provide['config.option', as_float()]) -> None:
+       ...
+
+
+   @inject
+   def foo(value: Decimal = Provide['config.option', as_(Decimal)]) -> None:
+       ...
+
+   @inject
+   def foo(value: str = Provide['config.option', required()]) -> None:
+       ...
+
+   @inject
+   def foo(value: int = Provide['config.option', required().as_int()]) -> None:
+       ...
+
+
+   @inject
+   def foo(value: int = Provide['config.option', invariant('config.switch')]) -> None:
+       ...
+
+   @inject
+   def foo(value: int = Provide['service', provided().foo['bar'].call()]) -> None:
+       ...
+
+
+To inject a container use special identifier ``<container>``:
+
+.. code-block:: python
+
+   @inject
+   def foo(container: Container = Provide['<container>']) -> None:
+       ...
+
 Wiring with modules and packages
 --------------------------------
 

examples/wiring/example_string_id.py

@@ -0,0 +1,27 @@
+"""Wiring string id example."""
+
+import sys
+
+from dependency_injector import containers, providers
+from dependency_injector.wiring import inject, Provide
+
+
+class Service:
+    ...
+
+
+class Container(containers.DeclarativeContainer):
+
+    service = providers.Factory(Service)
+
+
+@inject
+def main(service: Service = Provide['service']) -> None:
+    ...
+
+
+if __name__ == '__main__':
+    container = Container()
+    container.wire(modules=[sys.modules[__name__]])
+
+    main()

src/dependency_injector/wiring.py

@@ -50,6 +50,12 @@ class GenericMeta(type):
     'wire',
     'unwire',
     'inject',
+    'as_int',
+    'as_float',
+    'as_',
+    'required',
+    'invariant',
+    'provided',
     'Provide',
     'Provider',
     'Closing',
@@ -85,16 +91,23 @@ def get_from_module(self, module: ModuleType) -> Iterator[Callable[..., Any]]:
 
 class ProvidersMap:
 
+    CONTAINER_STRING_ID = '<container>'
+
     def __init__(self, container):
         self._container = container
         self._map = self._create_providers_map(
             current_container=container,
-            original_container=container.declarative_parent,
+            original_container=(
+                container.declarative_parent
+                if container.declarative_parent
+                else container
+            ),
         )
 
     def resolve_provider(
             self,
-            provider: providers.Provider,
+            provider: Union[providers.Provider, str],
+            modifier: Optional['Modifier'] = None,
     ) -> Optional[providers.Provider]:
         if isinstance(provider, providers.Delegate):
             return self._resolve_delegate(provider)
@@ -109,14 +122,29 @@ def resolve_provider(
             return self._resolve_config_option(provider)
         elif isinstance(provider, providers.TypedConfigurationOption):
             return self._resolve_config_option(provider.option, as_=provider.provides)
+        elif isinstance(provider, str):
+            return self._resolve_string_id(provider, modifier)
         else:
             return self._resolve_provider(provider)
 
-    def _resolve_delegate(
+    def _resolve_string_id(
             self,
-            original: providers.Delegate,
+            id: str,
+            modifier: Optional['Modifier'] = None,
     ) -> Optional[providers.Provider]:
-        return self._resolve_provider(original.provides)
+        if id == self.CONTAINER_STRING_ID:
+            return self._container.__self__
+
+        provider = self._container
+        for segment in id.split('.'):
+            try:
+                provider = getattr(provider, segment)
+            except AttributeError:
+                return None
+
+        if modifier:
+            provider = modifier.modify(provider, providers_map=self)
+        return provider
 
     def _resolve_provided_instance(
             self,
@@ -151,6 +179,12 @@ def _resolve_provided_instance(
 
         return new
 
+    def _resolve_delegate(
+            self,
+            original: providers.Delegate,
+    ) -> Optional[providers.Provider]:
+        return self._resolve_provider(original.provides)
+
     def _resolve_config_option(
             self,
             original: providers.ConfigurationOption,
@@ -184,7 +218,7 @@ def _resolve_provider(
         try:
             return self._map[original]
         except KeyError:
-            pass
+            return None
 
     @classmethod
     def _create_providers_map(
@@ -381,7 +415,7 @@ def _fetch_reference_injections(
 
 def _bind_injections(fn: Callable[..., Any], providers_map: ProvidersMap) -> None:
     for injection, marker in fn.__reference_injections__.items():
-        provider = providers_map.resolve_provider(marker.provider)
+        provider = providers_map.resolve_provider(marker.provider, marker.modifier)
 
         if provider is None:
             continue
@@ -516,20 +550,161 @@ def _is_declarative_container(instance: Any) -> bool:
             and getattr(instance, 'declarative_parent', None) is None)
 
 
+class Modifier:
+
+    def modify(
+            self,
+            provider: providers.ConfigurationOption,
+            providers_map: ProvidersMap,
+    ) -> providers.Provider:
+        ...
+
+
+class TypeModifier(Modifier):
+
+    def __init__(self, type_: Type):
+        self.type_ = type_
+
+    def modify(
+            self,
+            provider: providers.ConfigurationOption,
+            providers_map: ProvidersMap,
+    ) -> providers.Provider:
+        return provider.as_(self.type_)
+
+
+def as_int() -> TypeModifier:
+    """Return int type modifier."""
+    return TypeModifier(int)
+
+
+def as_float() -> TypeModifier:
+    """Return float type modifier."""
+    return TypeModifier(float)
+
+
+def as_(type_: Type) -> TypeModifier:
+    """Return custom type modifier."""
+    return TypeModifier(type_)
+
+
+class RequiredModifier(Modifier):
+
+    def __init__(self):
+        self.type_modifier = None
+
+    def as_int(self) -> 'RequiredModifier':
+        self.type_modifier = TypeModifier(int)
+        return self
+
+    def as_float(self) -> 'RequiredModifier':
+        self.type_modifier = TypeModifier(float)
+        return self
+
+    def as_(self, type_: Type) -> 'RequiredModifier':
+        self.type_modifier = TypeModifier(type_)
+        return self
+
+    def modify(
+            self,
+            provider: providers.ConfigurationOption,
+            providers_map: ProvidersMap,
+    ) -> providers.Provider:
+        provider = provider.required()
+        if self.type_modifier:
+            provider = provider.as_(self.type_modifier.type_)
+        return provider
+
+
+def required() -> RequiredModifier:
+    """Return required modifier."""
+    return RequiredModifier()
+
+
+class InvariantModifier(Modifier):
+
+    def __init__(self, id: str) -> None:
+        self.id = id
+
+    def modify(
+            self,
+            provider: providers.ConfigurationOption,
+            providers_map: ProvidersMap,
+    ) -> providers.Provider:
+        invariant_segment = providers_map.resolve_provider(self.id)
+        return provider[invariant_segment]
+
+
+def invariant(id: str) -> InvariantModifier:
+    """Return invariant modifier."""
+    return InvariantModifier(id)
+
+
+class ProvidedInstance(Modifier):
+
+    TYPE_ATTRIBUTE = 'attr'
+    TYPE_ITEM = 'item'
+    TYPE_CALL = 'call'
+
+    def __init__(self):
+        self.segments = []
+
+    def __getattr__(self, item):
+        self.segments.append((self.TYPE_ATTRIBUTE, item))
+        return self
+
+    def __getitem__(self, item):
+        self.segments.append((self.TYPE_ITEM, item))
+        return self
+
+    def call(self):
+        self.segments.append((self.TYPE_CALL, None))
+        return self
+
+    def modify(
+            self,
+            provider: providers.ConfigurationOption,
+            providers_map: ProvidersMap,
+    ) -> providers.Provider:
+        provider = provider.provided
+        for type_, value in self.segments:
+            if type_ == ProvidedInstance.TYPE_ATTRIBUTE:
+                provider = getattr(provider, value)
+            elif type_ == ProvidedInstance.TYPE_ITEM:
+                provider = provider[value]
+            elif type_ == ProvidedInstance.TYPE_CALL:
+                provider = provider.call()
+        return provider
+
+
+def provided() -> ProvidedInstance:
+    """Return provided instance modifier."""
+    return ProvidedInstance()
+
+
 class ClassGetItemMeta(GenericMeta):
     def __getitem__(cls, item):
         # Spike for Python 3.6
+        if isinstance(item, tuple):
+            return cls(*item)
         return cls(item)
 
 
 class _Marker(Generic[T], metaclass=ClassGetItemMeta):
 
-    def __init__(self, provider: Union[providers.Provider, Container]) -> None:
+    def __init__(
+            self,
+            provider: Union[providers.Provider, Container, str],
+            modifier: Optional[Modifier] = None,
+    ) -> None:
         if _is_declarative_container(provider):
             provider = provider.__self__
-        self.provider: providers.Provider = provider
+        self.provider = provider
+        self.modifier = modifier
 
     def __class_getitem__(cls, item) -> T:
+        if isinstance(item, tuple):
+            return cls(*item)
         return cls(item)
 
     def __call__(self) -> T: