The ExpressionLanguage can be extended by adding custom functions. For

instance, in theframework, the security has custom functions to check the

user's role.

instance, in theSymfony Framework, the security has custom functions to check

theuser's role.

..note::

If you want to learn how to use functions in an expression, read

":ref:`component-expression-functions`".

Register Functions

Registering Functions

Functionswill beregistered onthe current ``ExpressionLanguage`` instance.

Functionsareregistered oneach specific ``ExpressionLanguage`` instance.

That means the functions can be used in any expression executed by that

instance.

This will print ``hello``.

Creating a new ExpressionLanguageclass

Creating a new ExpressionLanguageClass

When you use the ``ExpressionLanguage`` class in your library, it's recommend

to create a new ``ExpressionLanguage`` class and register the functions there.

The class will execute ``registerFunctions`` to register the default

functions, you can override this to also add your own functions::

Override ``registerFunctions`` to add your own functions::

You can also use registered functions in the expression by using the same

syntax as PHP and JavaScript. The ExpressionLanguage component comes with one

function by default: ``constant()`` Which will return the value of the PHP

function by default: ``constant()``, which will return the value of the PHP

constant::

..tip::

To read how to register your ownfunction to use in an expression, see

To read how to register your ownfunctions to use in an expression, see

":doc:`/components/expression_language/extending`".

.. _component-expression-arrays:

This will evaluate to ``true``, because ``user.age`` is in the range from

``18``till ``45``

``18``to ``45``.

Ternary Operators