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The Contracts Component

The Contracts component provides a set of abstractions extracted out of the Symfony components. They can be used to build on semantics that the Symfony components proved useful - and that already have battle-tested implementations.

Installation

Contracts are provided as separate packages, so you can install only the ones your projects really need:

$ composer require symfony/cache-contracts
$ composer require symfony/event-dispatcher-contracts
$ composer require symfony/deprecation-contracts
$ composer require symfony/http-client-contracts
$ composer require symfony/service-contracts
$ composer require symfony/translation-contracts

Usage

The abstractions in this package are useful to achieve loose coupling and interoperability. By using the provided interfaces as type hints, you are able to reuse any implementations that match their contracts. It could be a Symfony component, or another package provided by the PHP community at large.

Depending on their semantics, some interfaces can be combined with :doc:`autowiring </service_container/autowiring>` to seamlessly inject a service in your classes.

Others might be useful as labeling interfaces, to hint about a specific behavior that can be enabled when using :ref:`autoconfiguration <services-autoconfigure>` or manual :doc:`service tagging </service_container/tags>` (or any other means provided by your framework.)

Design Principles

  • Contracts are split by domain, each into their own sub-namespaces;
  • Contracts are small and consistent sets of PHP interfaces, traits, normative docblocks and reference test suites when applicable, ...;
  • Contracts must have a proven implementation to enter this repository;
  • Contracts must be backward compatible with existing Symfony components.

Packages that implement specific contracts should list them in the provide section of their composer.json file, using the symfony/*-implementation convention. For example:

{
    "...": "...",
    "provide": {
        "symfony/cache-implementation": "3.0"
    }
}

Frequently Asked Questions

How Is this Different From PHP-FIG's PSRs?

When applicable, the provided contracts are built on top of PHP-FIG's PSRs. However, PHP-FIG has different goals and different processes. Symfony Contracts focuses on providing abstractions that are useful on their own while still compatible with implementations provided by Symfony.