.. index::

single: Caching; ExpressionLanguage

Caching Expressions Using ParserCaches

The ExpressionLanguage component already provides a

:method:`Symfony\\Component\\ExpresionLanguage\\ExpressionLanguage::compile`

method to be able to cache the expressions in plain PHP. But internally, the

component also caches the parsed expressions, so duplicated expressions can be

compiled/evaluated quicker.

The Workflow

Both ``evaluate`` and ``compile`` needs to do some things before it can

provide the return values. For ``evaluate``, this overhead is even bigger.

Both methods need to tokenize and parse the expression. This is done by the

:method:`Symfony\\Component\\ExpressionLanguage\\ExpressionLanguage::parse`

method. It'll return a :class:`Symfony\\Component\\ExpressionLanguage\\ParsedExpression`.

Now, the ``compile`` method just returns the string conversion of this object.

The ``evaluate`` method needs to loop through the "nodes" (pieces of an

expression saved in the ``ParsedExpression``) and evaluate them on the fly.

To save time, the ``ExpressionLanguage`` caches the ``ParsedExpression``, so

it can skip the tokenize and parse steps with duplicate expressions.

The caching is done by a

:class:`Symfony\\Component\\ExpressionLanguage\\ParserCache\\ParserCacheInterface`

instance (by default, it uses an

:class:`Symfony\\Component\\ExpressionLanguage\\ParserCache\\ArrayParserCache`).

You can customize this by creating a custom ``ParserCache`` and injecting this

in the object using the constructor::

.. note::

The `DoctrineBridge`_ has a ParserCache implementation using the

`doctrine cache library`_, which gives you caching for all sorts of cache

strategies, like Apc, Filesystem and Apc.

Using Parsed and Serialized Expressions

Both ``evaluate`` and ``compile`` can handle ``ParsedExpression`` and

``SerializedParsedExpression``::

.. code-block:: php

.. _DoctrineBridge: https://github.com/symfony/DoctrineBridge

.. _`doctrine cache library`: http://docs.doctrine-project.org/projects/doctrine-common/en/latest/reference/caching.html

caching

Caching

The component provides some different caching strategies, read more about them

in :doc:`/components/expression_language/caching`.

* :doc:`/components/expression_language/caching`