minor #7627 Update doc. Remove class ApcCache from doc (alexpts, javiereguiluz)

This PR was merged into the 3.2 branch.

Discussion
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Update doc. Remove class `ApcCache` from doc

Class `ApcCache` was deprecated since 2.5 and removed from 3.0 version. Update doc.

Commits
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7d4a554 Minor reword
9b9bb7c Update doc. Remove class `ApcCache` from doc

Author: xabbuh

components/validator/resources.rst

@@ -148,12 +148,18 @@ Caching
 Using many loaders to load metadata from different places is convenient, but it
 can slow down your application because each file needs to be parsed, validated
 and converted into a :class:`Symfony\\Component\\Validator\\Mapping\\ClassMetadata`
-instance. To solve this problem, you can cache the ``ClassMetadata`` information.
+instance.
 
-The Validator component comes with an
-:class:`Symfony\\Component\\Validator\\Mapping\\Cache\\ApcCache`
-implementation. You can easily create other cachers by creating a class which
-implements :class:`Symfony\\Component\\Validator\\Mapping\\Cache\\CacheInterface`.
+To solve this problem, call the :method:`Symfony\\Component\\Validator\\ValidatorBuilder::setMetadataCache`
+method of the Validator builder and pass your own caching class (which must
+implement :class:`Symfony\\Component\\Validator\\Mapping\\Cache\\CacheInterface`)::
+
+    use Symfony\Component\Validator\Validation;
+
+    $validator = Validation::createValidatorBuilder()
+        // ... add loaders
+        ->setMetadataCache(new SomeImplementCacheInterface());
+        ->getValidator();
 
 .. note::
 
@@ -163,18 +169,6 @@ implements :class:`Symfony\\Component\\Validator\\Mapping\\Cache\\CacheInterface
     the Validator still needs to merge all metadata of one class from every
     loader when it is requested.
 
-Enable the cache calling the
-:method:`Symfony\\Component\\Validator\\ValidatorBuilder::setMetadataCache`
-method of the Validator builder::
-
-    use Symfony\Component\Validator\Validation;
-    use Symfony\Component\Validator\Mapping\Cache\ApcCache;
-
-    $validator = Validation::createValidatorBuilder()
-        // ... add loaders
-        ->setMetadataCache(new ApcCache('some_apc_prefix'));
-        ->getValidator();
-
 Using a Custom MetadataFactory
 ------------------------------