Twig for Developers
This chapter describes the API to Twig and not the template language. It will be most useful as reference to those implementing the template interface to the application and not those who are creating Twig templates.
Basics
Twig uses a central object called the environment (of class
\Twig\Environment
). Instances of this class are used to store the
configuration and extensions, and are used to load templates.
Most applications create one \Twig\Environment
object on application
initialization and use that to load templates. In some cases, it might be useful
to have multiple environments side by side, with different configurations.
The typical way to configure Twig to load templates for an application looks roughly like this:
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require_once '/path/to/vendor/autoload.php';
$loader = new \Twig\Loader\FilesystemLoader('/path/to/templates');
$twig = new \Twig\Environment($loader, [
'cache' => '/path/to/compilation_cache',
]);
This creates a template environment with a default configuration and a loader
that looks up templates in the /path/to/templates/
directory. Different
loaders are available and you can also write your own if you want to load
templates from a database or other resources.
Note
Notice that the second argument of the environment is an array of options.
The cache
option is a compilation cache directory, where Twig caches
the compiled templates to avoid the parsing phase for sub-sequent
requests. It is very different from the cache you might want to add for
the evaluated templates. For such a need, you can use any available PHP
cache library.
Rendering Templates
To load a template from a Twig environment, call the load()
method which
returns a \Twig\TemplateWrapper
instance:
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$template = $twig->load('index.html');
To render the template with some variables, call the render()
method:
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echo $template->render(['the' => 'variables', 'go' => 'here']);
Note
The display()
method is a shortcut to output the rendered template.
You can also load and render the template in one fell swoop:
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echo $twig->render('index.html', ['the' => 'variables', 'go' => 'here']);
If a template defines blocks, they can be rendered individually via the
renderBlock()
call:
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echo $template->renderBlock('block_name', ['the' => 'variables', 'go' => 'here']);
Environment Options
When creating a new \Twig\Environment
instance, you can pass an array of
options as the constructor second argument:
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$twig = new \Twig\Environment($loader, ['debug' => true]);
The following options are available:
debug
booleanWhen set to
true
, the generated templates have a__toString()
method that you can use to display the generated nodes (default tofalse
).charset
string (defaults toutf-8
)The charset used by the templates.
base_template_class
string (defaults to\Twig\Template
)The base template class to use for generated templates.
cache
string orfalse
An absolute path where to store the compiled templates, or
false
to disable caching (which is the default).auto_reload
booleanWhen developing with Twig, it's useful to recompile the template whenever the source code changes. If you don't provide a value for the
auto_reload
option, it will be determined automatically based on thedebug
value.strict_variables
booleanIf set to
false
, Twig will silently ignore invalid variables (variables and or attributes/methods that do not exist) and replace them with anull
value. When set totrue
, Twig throws an exception instead (default tofalse
).autoescape
stringSets the default auto-escaping strategy (
name
,html
,js
,css
,url
,html_attr
, or a PHP callback that takes the template "filename" and returns the escaping strategy to use -- the callback cannot be a function name to avoid collision with built-in escaping strategies); set it tofalse
to disable auto-escaping. Thename
escaping strategy determines the escaping strategy to use for a template based on the template filename extension (this strategy does not incur any overhead at runtime as auto-escaping is done at compilation time.)optimizations
integerA flag that indicates which optimizations to apply (default to
-1
-- all optimizations are enabled; set it to0
to disable).
Loaders
Loaders are responsible for loading templates from a resource such as the file system.
Compilation Cache
All template loaders can cache the compiled templates on the filesystem for future reuse. It speeds up Twig a lot as templates are only compiled once.
Built-in Loaders
Here is a list of the built-in loaders:
\Twig\Loader\FilesystemLoader
\Twig\Loader\FilesystemLoader
loads templates from the file system. This loader
can find templates in folders on the file system and is the preferred way to
load them:
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$loader = new \Twig\Loader\FilesystemLoader($templateDir);
It can also look for templates in an array of directories:
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$loader = new \Twig\Loader\FilesystemLoader([$templateDir1, $templateDir2]);
With such a configuration, Twig will first look for templates in
$templateDir1
and if they do not exist, it will fallback to look for them
in the $templateDir2
.
You can add or prepend paths via the addPath()
and prependPath()
methods:
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$loader->addPath($templateDir3);
$loader->prependPath($templateDir4);
The filesystem loader also supports namespaced templates. This allows to group your templates under different namespaces which have their own template paths.
When using the setPaths()
, addPath()
, and prependPath()
methods,
specify the namespace as the second argument (when not specified, these
methods act on the "main" namespace):
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$loader->addPath($templateDir, 'admin');
Namespaced templates can be accessed via the special
@namespace_name/template_path
notation:
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$twig->render('@admin/index.html', []);
\Twig\Loader\FilesystemLoader
supports absolute and relative paths. Using relative
paths is preferred as it makes the cache keys independent of the project root
directory (for instance, it allows warming the cache from a build server where
the directory might be different from the one used on production servers):
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$loader = new \Twig\Loader\FilesystemLoader('templates', getcwd().'/..');
Note
When not passing the root path as a second argument, Twig uses getcwd()
for relative paths.
\Twig\Loader\ArrayLoader
\Twig\Loader\ArrayLoader
loads a template from a PHP array. It is passed an
array of strings bound to template names:
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$loader = new \Twig\Loader\ArrayLoader([
'index.html' => 'Hello {{ name }}!',
]);
$twig = new \Twig\Environment($loader);
echo $twig->render('index.html', ['name' => 'Fabien']);
This loader is very useful for unit testing. It can also be used for small projects where storing all templates in a single PHP file might make sense.
Tip
When using the Array
loader with a cache mechanism, you should know that
a new cache key is generated each time a template content "changes" (the
cache key being the source code of the template). If you don't want to see
your cache grows out of control, you need to take care of clearing the old
cache file by yourself.
\Twig\Loader\ChainLoader
\Twig\Loader\ChainLoader
delegates the loading of templates to other loaders:
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$loader1 = new \Twig\Loader\ArrayLoader([
'base.html' => '{% block content %}{% endblock %}',
]);
$loader2 = new \Twig\Loader\ArrayLoader([
'index.html' => '{% extends "base.html" %}{% block content %}Hello {{ name }}{% endblock %}',
'base.html' => 'Will never be loaded',
]);
$loader = new \Twig\Loader\ChainLoader([$loader1, $loader2]);
$twig = new \Twig\Environment($loader);
When looking for a template, Twig tries each loader in turn and returns as soon
as the template is found. When rendering the index.html
template from the
above example, Twig will load it with $loader2
but the base.html
template will be loaded from $loader1
.
Note
You can also add loaders via the addLoader()
method.
Create your own Loader
All loaders implement the \Twig\Loader\LoaderInterface
:
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interface \Twig\Loader\LoaderInterface
{
/**
* Returns the source context for a given template logical name.
*
* @param string $name The template logical name
*
* @return \Twig\Source
*
* @throws \Twig\Error\LoaderError When $name is not found
*/
public function getSourceContext($name);
/**
* Gets the cache key to use for the cache for a given template name.
*
* @param string $name The name of the template to load
*
* @return string The cache key
*
* @throws \Twig\Error\LoaderError When $name is not found
*/
public function getCacheKey($name);
/**
* Returns true if the template is still fresh.
*
* @param string $name The template name
* @param timestamp $time The last modification time of the cached template
*
* @return bool true if the template is fresh, false otherwise
*
* @throws \Twig\Error\LoaderError When $name is not found
*/
public function isFresh($name, $time);
/**
* Check if we have the source code of a template, given its name.
*
* @param string $name The name of the template to check if we can load
*
* @return bool If the template source code is handled by this loader or not
*/
public function exists($name);
}
The isFresh()
method must return true
if the current cached template
is still fresh, given the last modification time, or false
otherwise.
The getSourceContext()
method must return an instance of \Twig\Source
.
Using Extensions
Twig extensions are packages that add new features to Twig. Register an
extension via the addExtension()
method:
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$twig->addExtension(new \Twig\Extension\SandboxExtension());
Twig comes bundled with the following extensions:
- TwigExtensionCoreExtension: Defines all the core features of Twig.
- TwigExtensionDebugExtension: Defines the
dump
function to help debug template variables. - TwigExtensionEscaperExtension: Adds automatic output-escaping and the possibility to escape/unescape blocks of code.
- TwigExtensionSandboxExtension: Adds a sandbox mode to the default Twig environment, making it safe to evaluate untrusted code.
- TwigExtensionProfilerExtension: Enables the built-in Twig profiler.
- TwigExtensionOptimizerExtension: Optimizes the node tree before compilation.
- TwigExtensionStringLoaderExtension: Defines the
template_from_string
- function to allow loading templates from string in a template.
- TwigExtensionStringLoaderExtension: Defines the
The Core, Escaper, and Optimizer extensions are registered by default.
Built-in Extensions
This section describes the features added by the built-in extensions.
Tip
Read the chapter about extending Twig to learn how to create your own extensions.
Core Extension
The core
extension defines all the core features of Twig:
Escaper Extension
The escaper
extension adds automatic output escaping to Twig. It defines a
tag, autoescape
, and a filter, raw
.
When creating the escaper extension, you can switch on or off the global output escaping strategy:
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$escaper = new \Twig\Extension\EscaperExtension('html');
$twig->addExtension($escaper);
If set to html
, all variables in templates are escaped (using the html
escaping strategy), except those using the raw
filter:
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{{ article.to_html|raw }}
You can also change the escaping mode locally by using the autoescape
tag:
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{% autoescape 'html' %}
{{ var }}
{{ var|raw }} {# var won't be escaped #}
{{ var|escape }} {# var won't be double-escaped #}
{% endautoescape %}
Warning
The autoescape
tag has no effect on included files.
The escaping rules are implemented as follows:
Literals (integers, booleans, arrays, ...) used in the template directly as variables or filter arguments are never automatically escaped:
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{{ "Twig<br/>" }} {# won't be escaped #} {% set text = "Twig<br/>" %} {{ text }} {# will be escaped #}
Expressions which the result is a literal or a variable marked safe are never automatically escaped:
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{{ foo ? "Twig<br/>" : "<br/>Twig" }} {# won't be escaped #} {% set text = "Twig<br/>" %} {{ true ? text : "<br/>Twig" }} {# will be escaped #} {{ false ? text : "<br/>Twig" }} {# won't be escaped #} {% set text = "Twig<br/>" %} {{ foo ? text|raw : "<br/>Twig" }} {# won't be escaped #}
Objects with a
__toString
method are converted to strings and escaped. You can mark some classes and/or interfaces as being safe for some strategies viaEscaperExtension::addSafeClass()
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// mark object of class Foo as safe for the HTML strategy $escaper->addSafeClass('Foo', ['html']); // mark object of interface Foo as safe for the HTML strategy $escaper->addSafeClass('FooInterface', ['html']); // mark object of class Foo as safe for the HTML and JS strategies $escaper->addSafeClass('Foo', ['html', 'js']); // mark object of class Foo as safe for all strategies $escaper->addSafeClass('Foo', ['all']);
Escaping is applied before printing, after any other filter is applied:
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{{ var|upper }} {# is equivalent to {{ var|upper|escape }} #}
The `raw` filter should only be used at the end of the filter chain:
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{{ var|raw|upper }} {# will be escaped #} {{ var|upper|raw }} {# won't be escaped #}
Automatic escaping is not applied if the last filter in the chain is marked safe for the current context (e.g.
html
orjs
).escape
andescape('html')
are marked safe for HTML,escape('js')
is marked safe for JavaScript,raw
is marked safe for everything.1 2 3 4 5
{% autoescape 'js' %} {{ var|escape('html') }} {# will be escaped for HTML and JavaScript #} {{ var }} {# will be escaped for JavaScript #} {{ var|escape('js') }} {# won't be double-escaped #} {% endautoescape %}
Note
Note that autoescaping has some limitations as escaping is applied on
expressions after evaluation. For instance, when working with
concatenation, {{ foo|raw ~ bar }}
won't give the expected result as
escaping is applied on the result of the concatenation, not on the
individual variables (so, the raw
filter won't have any effect here).
Sandbox Extension
The sandbox
extension can be used to evaluate untrusted code. Access to
unsafe attributes and methods is prohibited. The sandbox security is managed
by a policy instance. By default, Twig comes with one policy class:
\Twig\Sandbox\SecurityPolicy
. This class allows you to white-list some
tags, filters, properties, and methods:
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$tags = ['if'];
$filters = ['upper'];
$methods = [
'Article' => ['getTitle', 'getBody'],
];
$properties = [
'Article' => ['title', 'body'],
];
$functions = ['range'];
$policy = new \Twig\Sandbox\SecurityPolicy($tags, $filters, $methods, $properties, $functions);
With the previous configuration, the security policy will only allow usage of
the if
tag, and the upper
filter. Moreover, the templates will only be
able to call the getTitle()
and getBody()
methods on Article
objects, and the title
and body
public properties. Everything else
won't be allowed and will generate a \Twig\Sandbox\SecurityError
exception.
The policy object is the first argument of the sandbox constructor:
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$sandbox = new \Twig\Extension\SandboxExtension($policy);
$twig->addExtension($sandbox);
By default, the sandbox mode is disabled and should be enabled when including
untrusted template code by using the sandbox
tag:
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{% sandbox %}
{% include 'user.html' %}
{% endsandbox %}
You can sandbox all templates by passing true
as the second argument of
the extension constructor:
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$sandbox = new \Twig\Extension\SandboxExtension($policy, true);
Profiler Extension
The profiler
extension enables a profiler for Twig templates; it should
only be used on your development machines as it adds some overhead:
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$profile = new \Twig\Profiler\Profile();
$twig->addExtension(new \Twig\Extension\ProfilerExtension($profile));
$dumper = new \Twig\Profiler\Dumper\TextDumper();
echo $dumper->dump($profile);
A profile contains information about time and memory consumption for template, block, and macro executions.
You can also dump the data in a Blackfire.io compatible format:
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$dumper = new \Twig\Profiler\Dumper\BlackfireDumper();
file_put_contents('/path/to/profile.prof', $dumper->dump($profile));
Upload the profile to visualize it (create a free account first):
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blackfire --slot=7 upload /path/to/profile.prof
Optimizer Extension
The optimizer
extension optimizes the node tree before compilation:
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$twig->addExtension(new \Twig\Extension\OptimizerExtension());
By default, all optimizations are turned on. You can select the ones you want to enable by passing them to the constructor:
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$optimizer = new \Twig\Extension\OptimizerExtension(\Twig\NodeVisitor\OptimizerNodeVisitor::OPTIMIZE_FOR);
$twig->addExtension($optimizer);
Twig supports the following optimizations:
\Twig\NodeVisitor\OptimizerNodeVisitor::OPTIMIZE_ALL
, enables all optimizations (this is the default value).\Twig\NodeVisitor\OptimizerNodeVisitor::OPTIMIZE_NONE
, disables all optimizations. This reduces the compilation time, but it can increase the execution time and the consumed memory.\Twig\NodeVisitor\OptimizerNodeVisitor::OPTIMIZE_FOR
, optimizes thefor
tag by removing theloop
variable creation whenever possible.\Twig\NodeVisitor\OptimizerNodeVisitor::OPTIMIZE_RAW_FILTER
, removes theraw
filter whenever possible.\Twig\NodeVisitor\OptimizerNodeVisitor::OPTIMIZE_VAR_ACCESS
, simplifies the creation and access of variables in the compiled templates whenever possible.
Exceptions
Twig can throw exceptions:
\Twig\Error\Error
: The base exception for all errors.\Twig\Error\SyntaxError
: Thrown to tell the user that there is a problem with the template syntax.\Twig\Error\RuntimeError
: Thrown when an error occurs at runtime (when a filter does not exist for instance).\Twig\Error\LoaderError
: Thrown when an error occurs during template loading.\Twig\Sandbox\SecurityError
: Thrown when an unallowed tag, filter, or method is called in a sandboxed template.