Conventions
===========

The :doc:`standards` document describes the coding standards for the Symfony
projects and the internal and third-party bundles. This document describes
coding standards and conventions used in the core framework to make it more
consistent and predictable. You are encouraged to follow them in your own
code, but you don't need to.

Method Names
------------

When an object has a "main" many relation with related "things"
(objects, parameters, ...), the method names are normalized:

* ``get()``
* ``set()``
* ``has()``
* ``all()``
* ``replace()``
* ``remove()``
* ``clear()``
* ``isEmpty()``
* ``add()``
* ``register()``
* ``count()``
* ``keys()``

The usage of these methods is only allowed when it is clear that there
is a main relation:

* a ``CookieJar`` has many ``Cookie`` objects;

* a Service ``Container`` has many services and many parameters (as services
  is the main relation, the naming convention is used for this relation);

* a Console ``Input`` has many arguments and many options. There is no "main"
  relation, and so the naming convention does not apply.

For many relations where the convention does not apply, the following methods
must be used instead (where ``XXX`` is the name of the related thing):

+----------------+-------------------+
| Main Relation  | Other Relations   |
+================+===================+
| ``get()``      | ``getXXX()``      |
+----------------+-------------------+
| ``set()``      | ``setXXX()``      |
+----------------+-------------------+
| n/a            | ``replaceXXX()``  |
+----------------+-------------------+
| ``has()``      | ``hasXXX()``      |
+----------------+-------------------+
| ``all()``      | ``getXXXs()``     |
+----------------+-------------------+
| ``replace()``  | ``setXXXs()``     |
+----------------+-------------------+
| ``remove()``   | ``removeXXX()``   |
+----------------+-------------------+
| ``clear()``    | ``clearXXX()``    |
+----------------+-------------------+
| ``isEmpty()``  | ``isEmptyXXX()``  |
+----------------+-------------------+
| ``add()``      | ``addXXX()``      |
+----------------+-------------------+
| ``register()`` | ``registerXXX()`` |
+----------------+-------------------+
| ``count()``    | ``countXXX()``    |
+----------------+-------------------+
| ``keys()``     | n/a               |
+----------------+-------------------+

.. note::

    While ``setXXX()`` and ``replaceXXX()`` are very similar, there is one notable
    difference: ``setXXX()`` may replace, or add new elements to the relation.
    ``replaceXXX()``, on the other hand, cannot add new elements. If an unrecognized
    key is passed to ``replaceXXX()`` it must throw an exception.

.. _contributing-code-conventions-deprecations:

Deprecating Code
----------------

From time to time, some classes and/or methods are deprecated in the
framework; that happens when a feature implementation cannot be changed
because of backward compatibility issues, but we still want to propose a
"better" alternative. In that case, the old implementation can be **deprecated**.

Deprecations must only be introduced on the next minor version of the impacted
component (or bundle, or bridge, or contract).
They can exceptionally be introduced on previous supported versions if they are critical.

A new class (or interface, or trait) cannot be introduced as deprecated, or
contain deprecated methods.

A new method cannot be introduced as deprecated.

A feature is marked as deprecated by adding a ``@deprecated`` PHPDoc to
relevant classes, methods, properties, ...::

    /**
     * @deprecated since Symfony 5.1.
     */

The deprecation message must indicate the version in which the feature was deprecated,
and whenever possible, how it was replaced::

    /**
     * @deprecated since Symfony 5.1, use Replacement instead.
     */

When the replacement is in another namespace than the deprecated class, its FQCN must be used::

    /**
     * @deprecated since Symfony 5.1, use A\B\Replacement instead.
     */

A deprecation must also be triggered to help people with the migration
(requires the ``symfony/deprecation-contracts`` package)::

    trigger_deprecation('symfony/package-name', '5.1', 'The "%s" class is deprecated, use "%s" instead.', Deprecated::class, Replacement::class);

When deprecating a whole class the ``trigger_error()`` call should be placed
after the use declarations, like in this example from `ServiceRouterLoader`_::

    namespace Symfony\Component\Routing\Loader\DependencyInjection;

    use Symfony\Component\Routing\Loader\ContainerLoader;

    trigger_deprecation('symfony/routing', '4.4', 'The "%s" class is deprecated, use "%s" instead.', ServiceRouterLoader::class, ContainerLoader::class);

    /**
     * @deprecated since Symfony 4.4, use Symfony\Component\Routing\Loader\ContainerLoader instead.
     */
    class ServiceRouterLoader extends ObjectRouteLoader

.. _`ServiceRouterLoader`: https://github.com/symfony/symfony/blob/4.4/src/Symfony/Component/Routing/Loader/DependencyInjection/ServiceRouterLoader.php

The deprecation must be added to the ``CHANGELOG.md`` file of the impacted component::

    4.4.0
    -----

    * Deprecated the `Deprecated` class, use `Replacement` instead.

It must also be added to the ``UPGRADE.md`` file of the targeted minor version
(``UPGRADE-4.4.md`` in our example)::

    DependencyInjection
    -------------------

    * Deprecated the `Deprecated` class, use `Replacement` instead.

Finally, its consequences must be added to the ``UPGRADE.md`` file of the next major version
(``UPGRADE-5.0.md`` in our example)::

    DependencyInjection
    -------------------

    * Removed the `Deprecated` class, use `Replacement` instead.

All these tasks are mandatory and must be done in the same pull request.

Removing Deprecated Code
------------------------

Removing deprecated code can only be done once every 2 years, on the next major version of the
impacted component (``master`` branch).

When removing deprecated code, the consequences of the deprecation must be added to the ``CHANGELOG.md`` file
of the impacted component::

    5.0.0
    -----

    * Removed the `Deprecated` class, use `Replacement` instead.

This task is mandatory and must be done in the same pull request.