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[DependencyInjection] Implementation/usage docs #6218

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43 changes: 43 additions & 0 deletions src/Symfony/Component/DependencyInjection/Definition.php
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Expand Up @@ -17,6 +17,49 @@
/**
* Definition represents a service definition.
*
* Scopes
*
* - ContainerInterface::SCOPE_CONTAINER: For the container scope (the default)
* the same instance is used each time you get the service.
* - ContainerInterface::SCOPE_PROTOTYPE: For the prototype scope a new instance
* is created each time you get the service.
* - Any string identifier: Whenever the specified scope name is entered, a new
* instance is created for the scope, and all instances of the scope are
* destroyed as soon as the scope is left.
* For instance, if you need to inject the request into your service, you need
* to define the scope of your service as 'request', so a new instance is
* created for each sub-request.
*
* Notes:
* - A service cannot have a dependency of a narrower scope, as the dependency
* would need to be changed otherwise.
* - A service can have a single scope only.
*
* @see Definition::setScope()
* @see Definition::getScope()
*
* Synthetic services
*
* A synthetic service is a service that is injected into the container instead
* of being created by the container.
*
* For instance, the request is injected by the HttpKernel in the handle()
* method when entering the 'request' scope. The purpose of the 'request' scope
* is to handle the fact that every subrequest is actually an entirely new
* request; i.e., any service that relies on the request needs to be re-created
* for every subrequest, because if the service would be re-used it would point
* to an outdated request. The purpose of scopes is to ensure that
* request-dependent services are not carried over to another (sub-)request.
*
* As a result, by default there is a synthetic 'request' service, which only
* exists to yield a better error message if the request service is retrieved
* outside of a 'request' scope. Before entering a 'request' scope, the kernel
* must be supplied with a Request service instance. Once the (sub-)request is
* complete, the scope is exited.
*
* @see Definition::setSynthetic()
* @see Definition::isSynthetic()
*
* @author Fabien Potencier <fabien@symfony.com>
*
* @api
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