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/lib/Twig/Autoloader.php'; Twig_Autoloader::register(); $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. .. 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. To load a template from this environment you just have to call the ``loadTemplate()`` method which then returns a ``Twig_Template`` instance:: $template = $twig->loadTemplate('index.html'); To render the template with some variables, call the ``render()`` method:: echo $template->render(array('the' => 'variables', 'go' => 'here')); .. note:: The ``display()`` method is a shortcut to output the template directly. You can also load and render the template in one fell swoop:: echo $twig->render('index.html', 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``: When set to ``true``, the generated templates have a ``__toString()`` method that you can use to display the generated nodes (default to ``false``). * ``charset``: The charset used by the templates (default to ``utf-8``). * ``base_template_class``: The base template class to use for generated templates (default to ``Twig_Template``). * ``cache``: An absolute path where to store the compiled templates, or ``false`` to disable caching (which is the default). * ``auto_reload``: 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``: 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``: If set to ``true``, auto-escaping will be enabled by default for all templates (default to ``true``). * ``optimizations``: 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``: 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``. * ``Twig_Loader_String``: Loads templates from a string. It's a dummy loader as you pass it the source code directly:: $loader = new Twig_Loader_String(); * ``Twig_Loader_Array``: Loads a template from a PHP array. It's passed an array of strings bound to template names. This loader is useful for unit testing:: $loader = new Twig_Loader_Array($templates); .. tip:: When using the ``Array`` or ``String`` loaders 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. Create your own Loader ~~~~~~~~~~~~~~~~~~~~~~ All loaders implement the ``Twig_LoaderInterface``:: interface Twig_LoaderInterface { /** * Gets the source code of a template, given its name. * * @param string $name string The name of the template to load * * @return string The template source code */ function getSource($name); /** * Gets the cache key to use for the cache for a given template name. * * @param string $name string The name of the template to load * * @return string The cache key */ function getCacheKey($name); /** * Returns true if the template is still fresh. * * @param string $name The template name * @param timestamp $time The last modification time of the cached template */ function isFresh($name, $time); } As an example, here is how the built-in ``Twig_Loader_String`` reads:: class Twig_Loader_String implements Twig_LoaderInterface { public function getSource($name) { return $name; } public function getCacheKey($name) { return $name; } public function isFresh($name, $time) { return false; } } The ``isFresh()`` method must return ``true`` if the current cached template is still fresh, given the last modification time, or ``false`` otherwise. 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 evaluated untrusted code. * *Twig_Extension_Optimizer*: Optimizers 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. You can disable an already registered extension:: $twig->removeExtension('escaper'); 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: * Tags: * ``for`` * ``if`` * ``extends`` * ``include`` * ``block`` * ``filter`` * ``macro`` * ``import`` * ``from`` * ``set`` * ``spaceless`` * Filters: * ``date`` * ``format`` * ``replace`` * ``url_encode`` * ``json_encode`` * ``title`` * ``capitalize`` * ``upper`` * ``lower`` * ``striptags`` * ``join`` * ``reverse`` * ``length`` * ``sort`` * ``merge`` * ``default`` * ``keys`` * ``escape`` * ``e`` * Functions: * ``range`` * ``constant`` * ``cycle`` * ``parent`` * ``block`` * Tests: * ``even`` * ``odd`` * ``defined`` * ``sameas`` * ``null`` * ``divisibleby`` * ``constant`` * ``empty`` Escaper Extension ~~~~~~~~~~~~~~~~~ The ``escaper`` extension adds automatic output escaping to Twig. It defines a new tag, ``autoescape``, and a new filter, ``raw``. When creating the escaper extension, you can switch on or off the global output escaping strategy:: $escaper = new Twig_Extension_Escaper(true); $twig->addExtension($escaper); If set to ``true``, all variables in templates are escaped, except those using the ``raw`` filter: .. code-block:: jinja {{ article.to_html|raw }} You can also change the escaping mode locally by using the ``autoescape`` tag: .. code-block:: jinja {% autoescape true %} {{ 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: .. code-block:: jinja {{ "Twig
" }} {# won't be escaped #} {% set text = "Twig
" %} {{ text }} {# will be escaped #} * Expressions which the result is always a literal or a variable marked safe are never automatically escaped: .. code-block:: jinja {{ foo ? "Twig
" : "
Twig" }} {# won't be escaped #} {% set text = "Twig
" %} {{ foo ? text : "
Twig" }} {# will be escaped #} {% set text = "Twig
" %} {{ foo ? text|raw : "
Twig" }} {# won't be escaped #} {% set text = "Twig
" %} {{ foo ? text|escape : "
Twig" }} {# the result of the expression won't be escaped #} * Escaping is applied before printing, after any other filter is applied: .. code-block:: jinja {{ var|upper }} {# is equivalent to {{ var|upper|escape }} #} * The `raw` filter should only be used at the end of the filter chain: .. code-block:: jinja {{ 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``). ``escaper`` and ``escaper('html')`` are marked safe for html, ``escaper('js')`` is marked safe for javascript, ``raw`` is marked safe for everything. .. code-block:: jinja {% autoescape true 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:: $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: .. code-block:: jinja {% 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); 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); 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.