Caution!
This section describes how to extend Twig as of Twig 1.12. If you are using an older version, read the :doc:`legacy<advanced_legacy>` chapter instead.
Twig can be extended in many ways; you can add extra tags, filters, tests, operators, global variables, and functions. You can even extend the parser itself with node visitors.
Note
The first section of this chapter describes how to extend Twig easily. If you want to reuse your changes in different projects or if you want to share them with others, you should then create an extension as described in the following section.
Caution!
When extending Twig without creating an extension, Twig won't be able to recompile your templates when the PHP code is updated. To see your changes in real-time, either disable template caching or package your code into an extension (see the next section of this chapter).
Before extending Twig, you must understand the differences between all the different possible extension points and when to use them.
First, remember that Twig has two main language constructs:
{{ }}: used to print the result of an expression evaluation;{% %}: used to execute statements.
To understand why Twig exposes so many extension points, let's see how to implement a Lorem ipsum generator (it needs to know the number of words to generate).
You can use a lipsum tag:
{% lipsum 40 %}That works, but using a tag for lipsum is not a good idea for at least
three main reasons:
lipsumis not a language construct;The tag outputs something;
The tag is not flexible as you cannot use it in an expression:
{{ 'some text' ~ {% lipsum 40 %} ~ 'some more text' }}
In fact, you rarely need to create tags; and that's good news because tags are the most complex extension point of Twig.
Now, let's use a lipsum filter:
{{ 40|lipsum }}Again, it works, but it looks weird. A filter transforms the passed value to
something else but here we use the value to indicate the number of words to
generate (so, 40 is an argument of the filter, not the value we want to
transform).
Next, let's use a lipsum function:
{{ lipsum(40) }}Here we go. For this specific example, the creation of a function is the extension point to use. And you can use it anywhere an expression is accepted:
{{ 'some text' ~ lipsum(40) ~ 'some more text' }}
{% set lipsum = lipsum(40) %}Last but not the least, you can also use a global object with a method able to generate lorem ipsum text:
{{ text.lipsum(40) }}As a rule of thumb, use functions for frequently used features and global objects for everything else.
Keep in mind the following when you want to extend Twig:
| What? | Implementation difficulty? | How often? | When? |
|---|---|---|---|
| macro | trivial | frequent | Content generation |
| global | trivial | frequent | Helper object |
| function | trivial | frequent | Content generation |
| filter | trivial | frequent | Value transformation |
| tag | complex | rare | DSL language construct |
| test | trivial | rare | Boolean decision |
| operator | trivial | rare | Values transformation |
A global variable is like any other template variable, except that it's available in all templates and macros:
$twig = new Twig_Environment($loader);
$twig->addGlobal('text', new Text());
You can then use the text variable anywhere in a template:
{{ text.lipsum(40) }}Creating a filter is as simple as associating a name with a PHP callable:
// an anonymous function
$filter = new Twig_SimpleFilter('rot13', function ($string) {
return str_rot13($string);
});
// or a simple PHP function
$filter = new Twig_SimpleFilter('rot13', 'str_rot13');
// or a class static method
$filter = new Twig_SimpleFilter('rot13', array('SomeClass', 'rot13Filter'));
$filter = new Twig_SimpleFilter('rot13', 'SomeClass::rot13Filter');
// or a class method
$filter = new Twig_SimpleFilter('rot13', array($this, 'rot13Filter'));
// the one below needs a runtime implementation (see below for more information)
$filter = new Twig_SimpleFilter('rot13', array('SomeClass', 'rot13Filter'));
The first argument passed to the Twig_SimpleFilter constructor is the name
of the filter you will use in templates and the second one is the PHP callable
to associate with it.
Then, add the filter to your Twig environment:
$twig = new Twig_Environment($loader); $twig->addFilter($filter);
And here is how to use it in a template:
{{ 'Twig'|rot13 }}
{# will output Gjvt #}When called by Twig, the PHP callable receives the left side of the filter
(before the pipe |) as the first argument and the extra arguments passed
to the filter (within parentheses ()) as extra arguments.
For instance, the following code:
{{ 'TWIG'|lower }}
{{ now|date('d/m/Y') }}is compiled to something like the following:
<?php echo strtolower('TWIG') ?>
<?php echo twig_date_format_filter($now, 'd/m/Y') ?>
The Twig_SimpleFilter class takes an array of options as its last
argument:
$filter = new Twig_SimpleFilter('rot13', 'str_rot13', $options);
If you want to access the current environment instance in your filter, set the
needs_environment option to true; Twig will pass the current
environment as the first argument to the filter call:
$filter = new Twig_SimpleFilter('rot13', function (Twig_Environment $env, $string) {
// get the current charset for instance
$charset = $env->getCharset();
return str_rot13($string);
}, array('needs_environment' => true));
If you want to access the current context in your filter, set the
needs_context option to true; Twig will pass the current context as
the first argument to the filter call (or the second one if
needs_environment is also set to true):
$filter = new Twig_SimpleFilter('rot13', function ($context, $string) {
// ...
}, array('needs_context' => true));
$filter = new Twig_SimpleFilter('rot13', function (Twig_Environment $env, $context, $string) {
// ...
}, array('needs_context' => true, 'needs_environment' => true));
If automatic escaping is enabled, the output of the filter may be escaped
before printing. If your filter acts as an escaper (or explicitly outputs HTML
or JavaScript code), you will want the raw output to be printed. In such a
case, set the is_safe option:
$filter = new Twig_SimpleFilter('nl2br', 'nl2br', array('is_safe' => array('html')));
Some filters may need to work on input that is already escaped or safe, for
example when adding (safe) HTML tags to originally unsafe output. In such a
case, set the pre_escape option to escape the input data before it is run
through your filter:
$filter = new Twig_SimpleFilter('somefilter', 'somefilter', array('pre_escape' => 'html', 'is_safe' => array('html')));
.. versionadded:: 1.19
Support for variadic filters was added in Twig 1.19.
When a filter should accept an arbitrary number of arguments, set the
is_variadic option to true; Twig will pass the extra arguments as the
last argument to the filter call as an array:
$filter = new Twig_SimpleFilter('thumbnail', function ($file, array $options = array()) {
// ...
}, array('is_variadic' => true));
Be warned that named arguments passed to a variadic filter cannot be checked for validity as they will automatically end up in the option array.
A filter name containing the special * character is a dynamic filter as
the * can be any string:
$filter = new Twig_SimpleFilter('*_path', function ($name, $arguments) {
// ...
});
The following filters will be matched by the above defined dynamic filter:
product_pathcategory_path
A dynamic filter can define more than one dynamic parts:
$filter = new Twig_SimpleFilter('*_path_*', function ($name, $suffix, $arguments) {
// ...
});
The filter will receive all dynamic part values before the normal filter
arguments, but after the environment and the context. For instance, a call to
'foo'|a_path_b() will result in the following arguments to be passed to
the filter: ('a', 'b', 'foo').
.. versionadded:: 1.21
Support for deprecated filters was added in Twig 1.21.
You can mark a filter as being deprecated by setting the deprecated option
to true. You can also give an alternative filter that replaces the
deprecated one when that makes sense:
$filter = new Twig_SimpleFilter('obsolete', function () {
// ...
}, array('deprecated' => true, 'alternative' => 'new_one'));
When a filter is deprecated, Twig emits a deprecation notice when compiling a template using it. See :ref:`deprecation-notices` for more information.
Functions are defined in the exact same way as filters, but you need to create
an instance of Twig_SimpleFunction:
$twig = new Twig_Environment($loader);
$function = new Twig_SimpleFunction('function_name', function () {
// ...
});
$twig->addFunction($function);
Functions support the same features as filters, except for the pre_escape
and preserves_safety options.
Tests are defined in the exact same way as filters and functions, but you need
to create an instance of Twig_SimpleTest:
$twig = new Twig_Environment($loader);
$test = new Twig_SimpleTest('test_name', function () {
// ...
});
$twig->addTest($test);
Tests allow you to create custom application specific logic for evaluating boolean conditions. As a simple example, let's create a Twig test that checks if objects are 'red':
$twig = new Twig_Environment($loader);
$test = new Twig_SimpleTest('red', function ($value) {
if (isset($value->color) && $value->color == 'red') {
return true;
}
if (isset($value->paint) && $value->paint == 'red') {
return true;
}
return false;
});
$twig->addTest($test);
Test functions should always return true/false.
When creating tests you can use the node_class option to provide custom test
compilation. This is useful if your test can be compiled into PHP primitives.
This is used by many of the tests built into Twig:
$twig = new Twig_Environment($loader);
$test = new Twig_SimpleTest(
'odd',
null,
array('node_class' => 'Twig_Node_Expression_Test_Odd'));
$twig->addTest($test);
class Twig_Node_Expression_Test_Odd extends Twig_Node_Expression_Test
{
public function compile(Twig_Compiler $compiler)
{
$compiler
->raw('(')
->subcompile($this->getNode('node'))
->raw(' % 2 == 1')
->raw(')')
;
}
}
The above example shows how you can create tests that use a node class. The
node class has access to one sub-node called 'node'. This sub-node contains the
value that is being tested. When the odd filter is used in code such as:
{% if my_value is odd %}The node sub-node will contain an expression of my_value. Node-based
tests also have access to the arguments node. This node will contain the
various other arguments that have been provided to your test.
If you want to pass a variable number of positional or named arguments to the
test, set the is_variadic option to true. Tests also support dynamic
name feature as filters and functions.
One of the most exciting features of a template engine like Twig is the possibility to define new language constructs. This is also the most complex feature as you need to understand how Twig's internals work.
Let's create a simple set tag that allows the definition of simple
variables from within a template. The tag can be used like follows:
{% set name = "value" %}
{{ name }}
{# should output value #}Note
The set tag is part of the Core extension and as such is always
available. The built-in version is slightly more powerful and supports
multiple assignments by default (cf. the template designers chapter for
more information).
Three steps are needed to define a new tag:
- Defining a Token Parser class (responsible for parsing the template code);
- Defining a Node class (responsible for converting the parsed code to PHP);
- Registering the tag.
Adding a tag is as simple as calling the addTokenParser method on the
Twig_Environment instance:
$twig = new Twig_Environment($loader); $twig->addTokenParser(new Project_Set_TokenParser());
Now, let's see the actual code of this class:
class Project_Set_TokenParser extends Twig_TokenParser
{
public function parse(Twig_Token $token)
{
$parser = $this->parser;
$stream = $parser->getStream();
$name = $stream->expect(Twig_Token::NAME_TYPE)->getValue();
$stream->expect(Twig_Token::OPERATOR_TYPE, '=');
$value = $parser->getExpressionParser()->parseExpression();
$stream->expect(Twig_Token::BLOCK_END_TYPE);
return new Project_Set_Node($name, $value, $token->getLine(), $this->getTag());
}
public function getTag()
{
return 'set';
}
}
The getTag() method must return the tag we want to parse, here set.
The parse() method is invoked whenever the parser encounters a set
tag. It should return a Twig_Node instance that represents the node (the
Project_Set_Node calls creating is explained in the next section).
The parsing process is simplified thanks to a bunch of methods you can call
from the token stream ($this->parser->getStream()):
getCurrent(): Gets the current token in the stream.next(): Moves to the next token in the stream, but returns the old one.test($type),test($value)ortest($type, $value): Determines whether the current token is of a particular type or value (or both). The value may be an array of several possible values.expect($type[, $value[, $message]]): If the current token isn't of the given type/value a syntax error is thrown. Otherwise, if the type and value are correct, the token is returned and the stream moves to the next token.look(): Looks a the next token without consuming it.
Parsing expressions is done by calling the parseExpression() like we did for
the set tag.
Tip
Reading the existing TokenParser classes is the best way to learn all
the nitty-gritty details of the parsing process.
The Project_Set_Node class itself is rather simple:
class Project_Set_Node extends Twig_Node
{
public function __construct($name, Twig_Node_Expression $value, $line, $tag = null)
{
parent::__construct(array('value' => $value), array('name' => $name), $line, $tag);
}
public function compile(Twig_Compiler $compiler)
{
$compiler
->addDebugInfo($this)
->write('$context[\''.$this->getAttribute('name').'\'] = ')
->subcompile($this->getNode('value'))
->raw(";\n")
;
}
}
The compiler implements a fluid interface and provides methods that helps the developer generate beautiful and readable PHP code:
subcompile(): Compiles a node.raw(): Writes the given string as is.write(): Writes the given string by adding indentation at the beginning of each line.string(): Writes a quoted string.repr(): Writes a PHP representation of a given value (seeTwig_Node_Forfor a usage example).addDebugInfo(): Adds the line of the original template file related to the current node as a comment.indent(): Indents the generated code (seeTwig_Node_Blockfor a usage example).outdent(): Outdents the generated code (seeTwig_Node_Blockfor a usage example).
The main motivation for writing an extension is to move often used code into a reusable class like adding support for internationalization. An extension can define tags, filters, tests, operators, global variables, functions, and node visitors.
Most of the time, it is useful to create a single extension for your project, to host all the specific tags and filters you want to add to Twig.
Tip
When packaging your code into an extension, Twig is smart enough to
recompile your templates whenever you make a change to it (when
auto_reload is enabled).
Note
Before writing your own extensions, have a look at the Twig official extension repository: http://github.com/twigphp/Twig-extensions.
An extension is a class that implements the following interface:
interface Twig_ExtensionInterface
{
/**
* Initializes the runtime environment.
*
* This is where you can load some file that contains filter functions for instance.
*
* @param Twig_Environment $environment The current Twig_Environment instance
*
* @deprecated since 1.23 (to be removed in 2.0), implement Twig_Extension_InitRuntimeInterface instead
*/
function initRuntime(Twig_Environment $environment);
/**
* Returns the token parser instances to add to the existing list.
*
* @return array An array of Twig_TokenParserInterface or Twig_TokenParserBrokerInterface instances
*/
function getTokenParsers();
/**
* Returns the node visitor instances to add to the existing list.
*
* @return array An array of Twig_NodeVisitorInterface instances
*/
function getNodeVisitors();
/**
* Returns a list of filters to add to the existing list.
*
* @return array An array of filters
*/
function getFilters();
/**
* Returns a list of tests to add to the existing list.
*
* @return array An array of tests
*/
function getTests();
/**
* Returns a list of functions to add to the existing list.
*
* @return array An array of functions
*/
function getFunctions();
/**
* Returns a list of operators to add to the existing list.
*
* @return array An array of operators
*/
function getOperators();
/**
* Returns a list of global variables to add to the existing list.
*
* @return array An array of global variables
*
* @deprecated since 1.23 (to be removed in 2.0), implement Twig_Extension_GlobalsInterface instead
*/
function getGlobals();
/**
* Returns the name of the extension.
*
* @return string The extension name
*
* @deprecated since 1.26 (to be removed in 2.0), not used anymore internally
*/
function getName();
}
To keep your extension class clean and lean, inherit from the built-in
Twig_Extension class instead of implementing the interface as it provides
empty implementations for all methods:
class Project_Twig_Extension extends Twig_Extension { }
Of course, this extension does nothing for now. We will customize it in the next sections.
Note
Prior to Twig 1.26, you must implement the getName() method which must
return a unique identifier for the extension.
Twig does not care where you save your extension on the filesystem, as all extensions must be registered explicitly to be available in your templates.
You can register an extension by using the addExtension() method on your
main Environment object:
$twig = new Twig_Environment($loader); $twig->addExtension(new Project_Twig_Extension());
Tip
The Twig core extensions are great examples of how extensions work.
Global variables can be registered in an extension via the getGlobals()
method:
class Project_Twig_Extension extends Twig_Extension implements Twig_Extension_GlobalsInterface
{
public function getGlobals()
{
return array(
'text' => new Text(),
);
}
// ...
}
Functions can be registered in an extension via the getFunctions()
method:
class Project_Twig_Extension extends Twig_Extension
{
public function getFunctions()
{
return array(
new Twig_SimpleFunction('lipsum', 'generate_lipsum'),
);
}
// ...
}
To add a filter to an extension, you need to override the getFilters()
method. This method must return an array of filters to add to the Twig
environment:
class Project_Twig_Extension extends Twig_Extension
{
public function getFilters()
{
return array(
new Twig_SimpleFilter('rot13', 'str_rot13'),
);
}
// ...
}
Adding a tag in an extension can be done by overriding the
getTokenParsers() method. This method must return an array of tags to add
to the Twig environment:
class Project_Twig_Extension extends Twig_Extension
{
public function getTokenParsers()
{
return array(new Project_Set_TokenParser());
}
// ...
}
In the above code, we have added a single new tag, defined by the
Project_Set_TokenParser class. The Project_Set_TokenParser class is
responsible for parsing the tag and compiling it to PHP.
The getOperators() methods lets you add new operators. Here is how to add
!, ||, and && operators:
class Project_Twig_Extension extends Twig_Extension
{
public function getOperators()
{
return array(
array(
'!' => array('precedence' => 50, 'class' => 'Twig_Node_Expression_Unary_Not'),
),
array(
'||' => array('precedence' => 10, 'class' => 'Twig_Node_Expression_Binary_Or', 'associativity' => Twig_ExpressionParser::OPERATOR_LEFT),
'&&' => array('precedence' => 15, 'class' => 'Twig_Node_Expression_Binary_And', 'associativity' => Twig_ExpressionParser::OPERATOR_LEFT),
),
);
}
// ...
}
The getTests() method lets you add new test functions:
class Project_Twig_Extension extends Twig_Extension
{
public function getTests()
{
return array(
new Twig_SimpleTest('even', 'twig_test_even'),
);
}
// ...
}
Twig filters, functions, and tests runtime implementations can be defined as any valid PHP callable:
- functions/static methods: Simple to implement and fast (used by all Twig core extensions); but it is hard for the runtime to depend on external objects;
- closures: Simple to implement;
- object methods: More flexible and required if your runtime code depends on external objects.
The simplest way to use methods is to define them on the extension itself:
class Project_Twig_Extension extends Twig_Extension
{
private $rot13Provider;
public function __construct($rot13Provider)
{
$this->rot13Provider = $rot13Provider;
}
public function getFunctions()
{
return array(
new Twig_SimpleFunction('rot13', array($this, 'rot13')),
);
}
public function rot13($value)
{
return $rot13Provider->rot13($value);
}
}
This is very convenient but not recommended as it makes template compilation depend on runtime dependencies even if they are not needed (think for instance as a dependency that connects to a database engine).
As of Twig 1.26, you can easily decouple the extension definitions from their
runtime implementations by registering a Twig_RuntimeLoaderInterface
instance on the environment that knows how to instantiate such runtime classes
(runtime classes must be autoload-able):
class RuntimeLoader implements Twig_RuntimeLoaderInterface
{
public function load($class)
{
// implement the logic to create an instance of $class
// and inject its dependencies
// most of the time, it means using your dependency injection container
if ('Project_Twig_RuntimeExtension' === $class) {
return new $class(new Rot13Provider());
} else {
// ...
}
}
}
$twig->addRuntimeLoader(new RuntimeLoader());
It is now possible to move the runtime logic to a new
Project_Twig_RuntimeExtension class and use it directly in the extension:
class Project_Twig_RuntimeExtension extends Twig_Extension
{
private $rot13Provider;
public function __construct($rot13Provider)
{
$this->rot13Provider = $rot13Provider;
}
public function rot13($value)
{
return $rot13Provider->rot13($value);
}
}
class Project_Twig_Extension extends Twig_Extension
{
public function getFunctions()
{
return array(
new Twig_SimpleFunction('rot13', array('Project_Twig_RuntimeExtension', 'rot13')),
// or
new Twig_SimpleFunction('rot13', 'Project_Twig_RuntimeExtension::rot13'),
);
}
}
To overload an already defined filter, test, operator, global variable, or function, re-define it in an extension and register it as late as possible (order matters):
class MyCoreExtension extends Twig_Extension
{
public function getFilters()
{
return array(
new Twig_SimpleFilter('date', array($this, 'dateFilter')),
);
}
public function dateFilter($timestamp, $format = 'F j, Y H:i')
{
// do something different from the built-in date filter
}
}
$twig = new Twig_Environment($loader);
$twig->addExtension(new MyCoreExtension());
Here, we have overloaded the built-in date filter with a custom one.
If you do the same on the Twig_Environment itself, beware that it takes
precedence over any other registered extensions:
$twig = new Twig_Environment($loader);
$twig->addFilter(new Twig_SimpleFilter('date', function ($timestamp, $format = 'F j, Y H:i') {
// do something different from the built-in date filter
}));
// the date filter will come from the above registration, not
// from the registered extension below
$twig->addExtension(new MyCoreExtension());
Caution!
Note that overloading the built-in Twig elements is not recommended as it might be confusing.
You can create functional tests for extensions simply by creating the following file structure in your test directory:
Fixtures/
filters/
foo.test
bar.test
functions/
foo.test
bar.test
tags/
foo.test
bar.test
IntegrationTest.php
The IntegrationTest.php file should look like this:
class Project_Tests_IntegrationTest extends Twig_Test_IntegrationTestCase
{
public function getExtensions()
{
return array(
new Project_Twig_Extension1(),
new Project_Twig_Extension2(),
);
}
public function getFixturesDir()
{
return dirname(__FILE__).'/Fixtures/';
}
}
Fixtures examples can be found within the Twig repository tests/Twig/Fixtures directory.
Testing the node visitors can be complex, so extend your test cases from
Twig_Test_NodeTestCase. Examples can be found in the Twig repository
tests/Twig/Node directory.