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 from the file system or other locations.

Most applications will create one Twig_Environment object on application initialization and use that to load templates. In some cases it's however useful to have multiple environments side by side, if different configurations are in use.

The simplest way to configure Twig to load templates for your application looks roughly like this:

require_once '/path/to/vendor/autoload.php';

$loader = new Twig_Loader_Filesystem('/path/to/templates');
$twig = new Twig_Environment($loader, array(
    'cache' => '/path/to/compilation_cache',
));

This will create a template environment with the default settings and a loader that looks up the templates in the /path/to/templates/ folder. Different loaders are available and you can also write your own if you want to load templates from a database or other resources.

Rendering Templates

To load a template from a Twig environment, call the load() method which returns a Twig_TemplateWrapper instance:

$template = $twig->load('index.html');

To render the template with some variables, call the render() method:

echo $template->render(array('the' => 'variables', 'go' => 'here'));

You can also load and render the template in one fell swoop:

echo $twig->render('index.html', array('the' => 'variables', 'go' => 'here'));

If a template defines blocks, they can be rendered individually via the renderBlock() call:

echo $template->renderBlock('block_name', array('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:

$twig = new Twig_Environment($loader, array('debug' => true));

The following options are available:

• debug boolean

  When set to true, the generated templates have a __toString() method that you can use to display the generated nodes (default to false).

• charset string (defaults to utf-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 or false

  An absolute path where to store the compiled templates, or false to disable caching (which is the default).

• auto_reload boolean

  When 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 the debug value.

• strict_variables boolean

  If set to false, Twig will silently ignore invalid variables (variables and or attributes/methods that do not exist) and replace them with a null value. When set to true, Twig throws an exception instead (default to false).

• autoescape string

  Sets 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 to false to disable auto-escaping. The name 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 integer

  A flag that indicates which optimizations to apply (default to -1 -- all optimizations are enabled; set it to 0 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; and the performance boost is even larger if you use a PHP accelerator such as APC. See the cache and auto_reload options of Twig_Environment above for more information.

Built-in Loaders

Here is a list of the built-in loaders Twig provides:

Twig_Loader_Filesystem

Twig_Loader_Filesystem 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:

$loader = new Twig_Loader_Filesystem($templateDir);

It can also look for templates in an array of directories:

$loader = new Twig_Loader_Filesystem(array($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:

$loader->addPath($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):

$loader->addPath($templateDir, 'admin');

Namespaced templates can be accessed via the special @namespace_name/template_path notation:

$twig->render('@admin/index.html', array());

Twig_Loader_Filesystem support 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):

$loader = new Twig_Loader_Filesystem('templates', getcwd().'/..');

Twig_Loader_Array

Twig_Loader_Array loads a template from a PHP array. It's passed an array of strings bound to template names:

$loader = new Twig_Loader_Array(array(
    'index.html' => 'Hello {{ name }}!',
));
$twig = new Twig_Environment($loader);

echo $twig->render('index.html', array('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.

Twig_Loader_Chain

Twig_Loader_Chain delegates the loading of templates to other loaders:

$loader1 = new Twig_Loader_Array(array(
    'base.html' => '{% block content %}{% endblock %}',
));
$loader2 = new Twig_Loader_Array(array(
    'index.html' => '{% extends "base.html" %}{% block content %}Hello {{ name }}{% endblock %}',
    'base.html'  => 'Will never be loaded',
));

$loader = new Twig_Loader_Chain(array($loader1, $loader2));

$twig = new Twig_Environment($loader);

When looking for a template, Twig will try each loader in turn and it will return 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.

Twig_Loader_Chain accepts any loader that implements Twig_LoaderInterface.

Create your own Loader

All loaders implement the Twig_LoaderInterface:

interface Twig_LoaderInterface
{
    /**
     * Returns the source context for a given template logical name.
     *
     * @param string $name The template logical name
     *
     * @return Twig_Source
     *
     * @throws Twig_Error_Loader 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_Loader 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_Loader 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. Using an extension is as simple as using the addExtension() method:

$twig->addExtension(new Twig_Extension_Sandbox());

Twig comes bundled with the following extensions:

• Twig_Extension_Core: Defines all the core features of Twig.
• Twig_Extension_Escaper: Adds automatic output-escaping and the possibility to escape/unescape blocks of code.
• Twig_Extension_Sandbox: Adds a sandbox mode to the default Twig environment, making it safe to evaluate untrusted code.
• Twig_Extension_Profiler: Enabled the built-in Twig profiler.
• Twig_Extension_Optimizer: Optimizes the node tree before compilation.

The core, escaper, and optimizer extensions do not need to be added to the Twig environment, as they are registered by default.

Built-in Extensions

This section describes the features added by the built-in extensions.

Core Extension

The core extension defines all the core features of Twig:

• Tags;
• Filters;
• Functions;
• Tests.

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:

$escaper = new Twig_Extension_Escaper('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:

{{ article.to_html|raw }}

You can also change the escaping mode locally by using the autoescape tag:

{% autoescape 'html' %}
    {{ var }}
    {{ var|raw }}      {# var won't be escaped #}
    {{ var|escape }}   {# var won't be double-escaped #}
{% endautoescape %}

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:

  {{ "Twig<br />" }} {# won't be escaped #}
  
  {% set text = "Twig<br />" %}
  {{ text }} {# will be escaped #}
  

• Expressions which the result is always a literal or a variable marked safe are never automatically escaped:

  {{ foo ? "Twig<br />" : "<br />Twig" }} {# won't be escaped #}
  
  {% set text = "Twig<br />" %}
  {{ foo ? text : "<br />Twig" }} {# will be escaped #}
  
  {% set text = "Twig<br />" %}
  {{ foo ? text|raw : "<br />Twig" }} {# won't be escaped #}
  
  {% set text = "Twig<br />" %}
  {{ foo ? text|escape : "<br />Twig" }} {# the result of the expression won't be escaped #}
  

• Escaping is applied before printing, after any other filter is applied:

  {{ var|upper }} {# is equivalent to {{ var|upper|escape }} #}
  

• The raw filter should only be used at the end of the filter chain:

  {{ 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 or js). escape and escape('html') are marked safe for HTML, escape('js') is marked safe for JavaScript, raw is marked safe for everything.

  {% 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 %}
  

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:

$tags = array('if');
$filters = array('upper');
$methods = array(
    'Article' => array('getTitle', 'getBody'),
);
$properties = array(
    'Article' => array('title', 'body'),
);
$functions = array('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:

$sandbox = new Twig_Extension_Sandbox($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:

{% sandbox %}
    {% include 'user.html' %}
{% endsandbox %}

You can sandbox all templates by passing true as the second argument of the extension constructor:

$sandbox = new Twig_Extension_Sandbox($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:

$profile = new Twig_Profiler_Profile();
$twig->addExtension(new Twig_Extension_Profiler($profile));

$dumper = new Twig_Profiler_Dumper_Text();
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:

$dumper = new Twig_Profiler_Dumper_Blackfire();
file_put_contents('/path/to/profile.prof', $dumper->dump($profile));

Upload the profile to visualize it (create a free account first):

blackfire --slot=7 upload /path/to/profile.prof

Optimizer Extension

The optimizer extension optimizes the node tree before compilation:

$twig->addExtension(new Twig_Extension_Optimizer());

By default, all optimizations are turned on. You can select the ones you want to enable by passing them to the constructor:

$optimizer = new Twig_Extension_Optimizer(Twig_NodeVisitor_Optimizer::OPTIMIZE_FOR);

$twig->addExtension($optimizer);

Twig supports the following optimizations:

• Twig_NodeVisitor_Optimizer::OPTIMIZE_ALL, enables all optimizations (this is the default value).
• Twig_NodeVisitor_Optimizer::OPTIMIZE_NONE, disables all optimizations. This reduces the compilation time, but it can increase the execution time and the consumed memory.
• Twig_NodeVisitor_Optimizer::OPTIMIZE_FOR, optimizes the for tag by removing the loop variable creation whenever possible.
• Twig_NodeVisitor_Optimizer::OPTIMIZE_RAW_FILTER, removes the raw filter whenever possible.
• Twig_NodeVisitor_Optimizer::OPTIMIZE_VAR_ACCESS, simplifies the creation and access of variables in the compiled templates whenever possible.

Exceptions

Twig can throw exceptions:

• Twig_Error: The base exception for all errors.
• Twig_Error_Syntax: Thrown to tell the user that there is a problem with the template syntax.
• Twig_Error_Runtime: Thrown when an error occurs at runtime (when a filter does not exist for instance).
• Twig_Error_Loader: 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.