Defining Services Dependencies Automatically

..versionadded::2.8

Support for autowiring services was introduced in Symfony 2.8.

Autowiring allows to register services in the container with minimal configuration.

It is useful in the field of `Rapid Application Development`_, when designing prototypes

in early stages of large projects. It makes it easy to register a service graph

and eases refactoring.

It automatically resolves the service dependencies based on the constructor's

typehint which is useful in the field of `Rapid Application Development`_,

when designing prototypes in early stages of large projects. It makes it easy

to register a service graph and eases refactoring.

Imagine you're building an API to publish statuses on a Twitter feed,obfuscated

with `ROT13`.. (a special case of the Caesar cipher).

Imagine you're building an API to publish statuses on a Twitter feed,which

has to be obfuscatedwith ``ROT13`` (a special case of the Caesar cipher).

Start by creating a ROT13 transformer class::

The Dependency Injection Component will be able to automatically register the dependencies

of this ``TwitterClient`` class by marking the ``twitter_client`` service as autowired:

The DependencyInjection component will be able to automatically register

the dependencies of this ``TwitterClient`` class when the ``twitter_client``

service is marked as autowired:

..configuration-block::

You can give a try to the API with ``curl``::

You can give the API a try using ``curl``:

..code-block::bash

It should return ``OK``.

..code-block::xml

It deserves some explanations. We now have 2 services implementing the ``TransformerInterface``.

The autowiring subsystem cannot guess which one to use, this leads to errors

like::

This deserves some explanations. You now have two services implementing the

``TransformerInterface``. The autowiring subsystem cannot guess which one

to use which leads to errors like this:

..code-block::text

Fortunately, the ``autowiring_types`` key is here to specify which implementation

to use by default. This key can take a list of types if necessary (using a YAML

array).

to use by default. This key can take a list of types if necessary.

Thanks to this setting, the ``rot13_transformer`` service is automatically injected

as an argument of the ``uppercase_rot13_transformer`` and ``twitter_client`` services. For