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minor #4748 Re-reading private service section (weaverryan)

This PR was merged into the 2.3 branch.

Discussion
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Re-reading private service section

| Q   | A
| --- | ---
| Doc fix? | yes
| New docs? | kind of
| Applies to | all
| Fixed tickets | n/a

Hi guys!

This follows #4656. I merged that, but then realized that if you read the wider section, the top was still talking about private services as if their benefit was to *not* allow fetching directly (whereas the true emphasis now is on performance, and how `get()` may or may not work.

Thanks!

Commits
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8f5e210 Re-wording based on Wouter's recommendation
0f86a86 [#4656] Re-reading private service section
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weaverryan committed Jan 4, 2015
2 parents d9935a3 + 8f5e210 commit 43543bb0fbb058898ea7f531601754ea9e0074a3
Showing with 17 additions and 19 deletions.
  1. +17 −19 components/dependency_injection/advanced.rst
@@ -10,29 +10,19 @@ Marking Services as public / private
When defining services, you'll usually want to be able to access these definitions
within your application code. These services are called ``public``. For example,
the ``doctrine`` service registered with the container when using the DoctrineBundle
is a public service as you can access it via::
is a public service. This means that you can fetch it from the container
using the ``get()`` method::
$doctrine = $container->get('doctrine');
However, there are use-cases when you don't want a service to be public. This
is common when a service is only defined because it could be used as an
argument for another service.
In some cases, a service *only* exists to be injected into another service
and is *not* intended to be fetched directly from the container as shown
above.
.. _inlined-private-services:
Since a container is not able to detect if a service is retrieved from inside
the container or the outside, a private service may still be retrieved using
the ``get()`` method.
What makes private services special, is that they are converted from services
to inlined instantiation (e.g. ``new PrivateThing()``) when they are only
injected once, to increase the container performance. This means that you can
never be sure if a private service exists in the container.
Simply said: A service will be private when you do not want to access it
directly from your code.
Here is an example:
In these cases, to get a minor performance boost, you can set the service
to be *not* public (i.e. private):
.. configuration-block::
@@ -63,11 +53,19 @@ Here is an example:
$definition->setPublic(false);
$container->setDefinition('foo', $definition);
Now that the service is private, you *should not* call (should not means, this
*might* fail, see the explaination above)::
What makes private services special is that, if they are only injected once,
they are converted from services to inlined instantiations (e.g. ``new PrivateThing()``).
This increases the container's performance.
Now that the service is private, you *should not* fetch the service directly
from the container::
$container->get('foo');
This *may or may not work*, depending on if the service could be inlined.
Simply said: A service can be marked as private if you do not want to access
it directly from your code.
However, if a service has been marked as private, you can still alias it (see
below) to access this service (via the alias).

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