Update docs

docs/providers/dependency.rst

@@ -8,13 +8,22 @@ Dependency provider
 To specify a type of the dependency use ``instance_of`` argument: ``Dependency(instance_of=SomeClass)``.
 Dependency provider will control that returned object is an instance of ``instance_of`` type.
 
-The ``Dependency`` provider must be overridden before usage. It can be overridden by any type of
-the provider. The only rule is that overriding provider must return an instance of ``instance_of``
-dependency type.
-
 .. literalinclude:: ../../examples/providers/dependency.py
    :language: python
    :lines: 3-
-   :emphasize-lines: 26
+   :emphasize-lines: 26,35-36
+
+To provide a dependency you need to override the ``Dependency`` provider. You can call
+provider ``.override()`` method or provide an overriding provider when creating a container.
+See :ref:`provider-overriding`.
+
+You also can provide a default for the dependency. To provide a default use ``default`` argument:
+``Dependency(..., default=...)``. Default can be a value or a provider. If default is not a provider,
+dependency provider will wrap it into the ``Object`` provider.
+
+.. literalinclude:: ../../examples/providers/dependency_default.py
+   :language: python
+   :lines: 16-23
+   :emphasize-lines: 3
 
 .. disqus::

examples/providers/dependency_default.py

@@ -0,0 +1,25 @@
+"""`Dependency` provider default example."""
+
+import abc
+
+from dependency_injector import containers, providers
+
+
+class Cache(metaclass=abc.ABCMeta):
+    ...
+
+
+class InMemoryCache(Cache):
+    ...
+
+
+class Container(containers.DeclarativeContainer):
+
+    cache = providers.Dependency(instance_of=Cache, default=InMemoryCache())
+
+
+if __name__ == '__main__':
+    container = Container()
+    cache = container.cache()  # provides InMemoryCache()
+
+    assert isinstance(cache, InMemoryCache)