Twig for Template Designers
===========================

This document describes the syntax and semantics of the template engine and
will be most useful as reference to those creating Twig templates.

Synopsis
--------

A template is a regular text file. It can generate any text-based format (HTML,
XML, CSV, LaTeX, etc.). It doesn't have a specific extension, ``.html`` or
``.xml`` are just fine.

A template contains **variables** or **expressions**, which get replaced with
values when the template is evaluated, and **tags**, which control the
template's logic.

Below is a minimal template that illustrates a few basics. We will cover further
details later on:

.. code-block:: html+twig

    <!DOCTYPE html>
    <html>
        <head>
            <title>My Webpage</title>
        </head>
        <body>
            <ul id="navigation">
            {% for item in navigation %}
                <li><a href="{{ item.href }}">{{ item.caption }}</a></li>
            {% endfor %}
            </ul>

            <h1>My Webpage</h1>
            {{ a_variable }}
        </body>
    </html>

There are two kinds of delimiters: ``{% ... %}`` and ``{{ ... }}``. The first
one is used to execute statements such as for-loops, the latter outputs the
result of an expression.

IDEs Integration
----------------

Many IDEs support syntax highlighting and auto-completion for Twig:

* *Textmate* via the `Twig bundle`_
* *Vim* via the `Jinja syntax plugin`_ or the `vim-twig plugin`_
* *Netbeans* via the `Twig syntax plugin`_ (until 7.1, native as of 7.2)
* *PhpStorm* (native as of 2.1)
* *Eclipse* via the `Twig plugin`_
* *Sublime Text* via the `Twig bundle`_
* *GtkSourceView* via the `Twig language definition`_ (used by gedit and other projects)
* *Coda* and *SubEthaEdit* via the `Twig syntax mode`_
* *Coda 2* via the `other Twig syntax mode`_
* *Komodo* and *Komodo Edit* via the Twig highlight/syntax check mode
* *Notepad++* via the `Notepad++ Twig Highlighter`_
* *Emacs* via `web-mode.el`_
* *Atom* via the `PHP-twig for atom`_
* *Visual Studio Code* via the `Twig pack`_

Also, `TwigFiddle`_ is an online service that allows you to execute Twig templates
from a browser; it supports all versions of Twig.

Variables
---------

The application passes variables to the templates for manipulation in the
template. Variables may have attributes or elements you can access, too. The
visual representation of a variable depends heavily on the application providing
it.

Use a dot (``.``) to access attributes of a variable (methods or properties of a
PHP object, or items of a PHP array):

.. code-block:: twig

    {{ foo.bar }}

.. note::

    It's important to know that the curly braces are *not* part of the
    variable but the print statement. When accessing variables inside tags,
    don't put the braces around them.

.. sidebar:: Implementation

    For convenience's sake ``foo.bar`` does the following things on the PHP
    layer:

    * check if ``foo`` is an array and ``bar`` a valid element;
    * if not, and if ``foo`` is an object, check that ``bar`` is a valid property;
    * if not, and if ``foo`` is an object, check that ``bar`` is a valid method
      (even if ``bar`` is the constructor - use ``__construct()`` instead);
    * if not, and if ``foo`` is an object, check that ``getBar`` is a valid method;
    * if not, and if ``foo`` is an object, check that ``isBar`` is a valid method;
    * if not, and if ``foo`` is an object, check that ``hasBar`` is a valid method;
    * if not, return a ``null`` value.

    Twig also supports a specific syntax for accessing items on PHP arrays,
    ``foo['bar']``:

    * check if ``foo`` is an array and ``bar`` a valid element;
    * if not, return a ``null`` value.

If a variable or attribute does not exist, you will receive a ``null`` value
when the ``strict_variables`` option is set to ``false``; alternatively, if ``strict_variables``
is set, Twig will throw an error (see :ref:`environment options<environment_options>`).

.. note::

    If you want to access a dynamic attribute of a variable, use the
    :doc:`attribute<functions/attribute>` function instead.

    The ``attribute`` function is also useful when the attribute contains
    special characters (like ``-`` that would be interpreted as the minus
    operator):

    .. code-block:: twig

        {# equivalent to the non-working foo.data-foo #}
        {{ attribute(foo, 'data-foo') }}

Global Variables
~~~~~~~~~~~~~~~~

The following variables are always available in templates:

* ``_self``: references the current template name;
* ``_context``: references the current context;
* ``_charset``: references the current charset.

Setting Variables
~~~~~~~~~~~~~~~~~

You can assign values to variables inside code blocks. Assignments use the
:doc:`set<tags/set>` tag:

.. code-block:: twig

    {% set foo = 'foo' %}
    {% set foo = [1, 2] %}
    {% set foo = {'foo': 'bar'} %}

Filters
-------

Variables can be modified by **filters**. Filters are separated from the
variable by a pipe symbol (``|``). Multiple filters can be chained. The output
of one filter is applied to the next.

The following example removes all HTML tags from the ``name`` and title-cases
it:

.. code-block:: twig

    {{ name|striptags|title }}

Filters that accept arguments have parentheses around the arguments. This
example joins the elements of a list by commas:

.. code-block:: twig

    {{ list|join(', ') }}

To apply a filter on a section of code, wrap it with the
:doc:`apply<tags/apply>` tag:

.. code-block:: twig

    {% apply upper %}
        This text becomes uppercase
    {% endapply %}

Go to the :doc:`filters<filters/index>` page to learn more about built-in
filters.

Functions
---------

Functions can be called to generate content. Functions are called by their
name followed by parentheses (``()``) and may have arguments.

For instance, the ``range`` function returns a list containing an arithmetic
progression of integers:

.. code-block:: twig

    {% for i in range(0, 3) %}
        {{ i }},
    {% endfor %}

Go to the :doc:`functions<functions/index>` page to learn more about the
built-in functions.

.. _named-arguments:

Named Arguments
---------------

.. code-block:: twig

    {% for i in range(low=1, high=10, step=2) %}
        {{ i }},
    {% endfor %}

Using named arguments makes your templates more explicit about the meaning of
the values you pass as arguments:

.. code-block:: twig

    {{ data|convert_encoding('UTF-8', 'iso-2022-jp') }}

    {# versus #}

    {{ data|convert_encoding(from='iso-2022-jp', to='UTF-8') }}

Named arguments also allow you to skip some arguments for which you don't want
to change the default value:

.. code-block:: twig

    {# the first argument is the date format, which defaults to the global date format if null is passed #}
    {{ "now"|date(null, "Europe/Paris") }}

    {# or skip the format value by using a named argument for the time zone #}
    {{ "now"|date(timezone="Europe/Paris") }}

You can also use both positional and named arguments in one call, in which
case positional arguments must always come before named arguments:

.. code-block:: twig

    {{ "now"|date('d/m/Y H:i', timezone="Europe/Paris") }}

.. tip::

    Each function and filter documentation page has a section where the names
    of all arguments are listed when supported.

Control Structure
-----------------

A control structure refers to all those things that control the flow of a
program - conditionals (i.e. ``if``/``elseif``/``else``), ``for``-loops, as
well as things like blocks. Control structures appear inside ``{% ... %}``
blocks.

For example, to display a list of users provided in a variable called
``users``, use the :doc:`for<tags/for>` tag:

.. code-block:: twig

    <h1>Members</h1>
    <ul>
        {% for user in users %}
            <li>{{ user.username|e }}</li>
        {% endfor %}
    </ul>

The :doc:`if<tags/if>` tag can be used to test an expression:

.. code-block:: twig

    {% if users|length > 0 %}
        <ul>
            {% for user in users %}
                <li>{{ user.username|e }}</li>
            {% endfor %}
        </ul>
    {% endif %}

Go to the :doc:`tags<tags/index>` page to learn more about the built-in tags.

Comments
--------

To comment-out part of a line in a template, use the comment syntax ``{# ...
#}``. This is useful for debugging or to add information for other template
designers or yourself:

.. code-block:: twig

    {# note: disabled template because we no longer use this
        {% for user in users %}
            ...
        {% endfor %}
    #}

Including other Templates
-------------------------

The :doc:`include<functions/include>` function is useful to include a template
and return the rendered content of that template into the current one:

.. code-block:: twig

    {{ include('sidebar.html') }}

By default, included templates have access to the same context as the template
which includes them. This means that any variable defined in the main template
will be available in the included template too:

.. code-block:: twig

    {% for box in boxes %}
        {{ include('render_box.html') }}
    {% endfor %}

The included template ``render_box.html`` is able to access the ``box`` variable.

The name of the template depends on the template loader. For instance, the
``\Twig\Loader\FilesystemLoader`` allows you to access other templates by giving the
filename. You can access templates in subdirectories with a slash:

.. code-block:: twig

    {{ include('sections/articles/sidebar.html') }}

This behavior depends on the application embedding Twig.

Template Inheritance
--------------------

The most powerful part of Twig is template inheritance. Template inheritance
allows you to build a base "skeleton" template that contains all the common
elements of your site and defines **blocks** that child templates can
override.

It's easier to understand the concept by starting with an example.

Let's define a base template, ``base.html``, which defines an HTML skeleton
document that might be used for a two-column page:

.. code-block:: html+twig

    <!DOCTYPE html>
    <html>
        <head>
            {% block head %}
                <link rel="stylesheet" href="style.css" />
                <title>{% block title %}{% endblock %} - My Webpage</title>
            {% endblock %}
        </head>
        <body>
            <div id="content">{% block content %}{% endblock %}</div>
            <div id="footer">
                {% block footer %}
                    &copy; Copyright 2011 by <a href="http://domain.invalid/">you</a>.
                {% endblock %}
            </div>
        </body>
    </html>

In this example, the :doc:`block<tags/block>` tags define four blocks that
child templates can fill in. All the ``block`` tag does is to tell the
template engine that a child template may override those portions of the
template.

A child template might look like this:

.. code-block:: twig

    {% extends "base.html" %}

    {% block title %}Index{% endblock %}
    {% block head %}
        {{ parent() }}
        <style type="text/css">
            .important { color: #336699; }
        </style>
    {% endblock %}
    {% block content %}
        <h1>Index</h1>
        <p class="important">
            Welcome to my awesome homepage.
        </p>
    {% endblock %}

The :doc:`extends<tags/extends>` tag is the key here. It tells the template
engine that this template "extends" another template. When the template system
evaluates this template, first it locates the parent. The extends tag should
be the first tag in the template.

Note that since the child template doesn't define the ``footer`` block, the
value from the parent template is used instead.

It's possible to render the contents of the parent block by using the
:doc:`parent<functions/parent>` function. This gives back the results of the
parent block:

.. code-block:: twig

    {% block sidebar %}
        <h3>Table Of Contents</h3>
        ...
        {{ parent() }}
    {% endblock %}

.. tip::

    The documentation page for the :doc:`extends<tags/extends>` tag describes
    more advanced features like block nesting, scope, dynamic inheritance, and
    conditional inheritance.

.. note::

    Twig also supports multiple inheritance via "horizontal reuse" with the help
    of the :doc:`use<tags/use>` tag.

HTML Escaping
-------------

When generating HTML from templates, there's always a risk that a variable
will include characters that affect the resulting HTML. There are two
approaches: manually escaping each variable or automatically escaping
everything by default.

Twig supports both, automatic escaping is enabled by default.

The automatic escaping strategy can be configured via the
:ref:`autoescape<environment_options>` option and defaults to ``html``.

Working with Manual Escaping
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If manual escaping is enabled, it is **your** responsibility to escape variables
if needed. What to escape? Any variable that comes from an untrusted source.

Escaping works by using the :doc:`escape<filters/escape>` or ``e`` filter:

.. code-block:: twig

    {{ user.username|e }}

By default, the ``escape`` filter uses the ``html`` strategy, but depending on
the escaping context, you might want to explicitly use an other strategy:

.. code-block:: twig

    {{ user.username|e('js') }}
    {{ user.username|e('css') }}
    {{ user.username|e('url') }}
    {{ user.username|e('html_attr') }}

Working with Automatic Escaping
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Whether automatic escaping is enabled or not, you can mark a section of a
template to be escaped or not by using the :doc:`autoescape<tags/autoescape>`
tag:

.. code-block:: twig

    {% autoescape %}
        Everything will be automatically escaped in this block (using the HTML strategy)
    {% endautoescape %}

By default, auto-escaping uses the ``html`` escaping strategy. If you output
variables in other contexts, you need to explicitly escape them with the
appropriate escaping strategy:

.. code-block:: twig

    {% autoescape 'js' %}
        Everything will be automatically escaped in this block (using the JS strategy)
    {% endautoescape %}

Escaping
--------

It is sometimes desirable or even necessary to have Twig ignore parts it would
otherwise handle as variables or blocks. For example if the default syntax is
used and you want to use ``{{`` as raw string in the template and not start a
variable you have to use a trick.

The easiest way is to output the variable delimiter (``{{``) by using a variable
expression:

.. code-block:: twig

    {{ '{{' }}

For bigger sections it makes sense to mark a block
:doc:`verbatim<tags/verbatim>`.

Macros
------

Macros are comparable with functions in regular programming languages. They are
useful to reuse HTML fragments to not repeat yourself. They are described in the
:doc:`macro<tags/macro>` tag documentation.

.. _twig-expressions:

Expressions
-----------

Twig allows expressions everywhere.

.. note::

    The operator precedence is as follows, with the lowest-precedence operators
    listed first: ``?:`` (ternary operator), ``b-and``, ``b-xor``, ``b-or``,
    ``or``, ``and``, ``==``, ``!=``, ``<=>``, ``<``, ``>``, ``>=``, ``<=``,
    ``in``, ``matches``, ``starts with``, ``ends with``, ``..``, ``+``, ``-``,
    ``~``, ``*``, ``/``, ``//``, ``%``, ``is`` (tests), ``**``, ``??``, ``|``
    (filters), ``[]``, and ``.``:

    .. code-block:: twig

        {% set greeting = 'Hello ' %}
        {% set name = 'Fabien' %}

        {{ greeting ~ name|lower }}   {# Hello fabien #}

        {# use parenthesis to change precedence #}
        {{ (greeting ~ name)|lower }} {# hello fabien #}

Literals
~~~~~~~~

The simplest form of expressions are literals. Literals are representations
for PHP types such as strings, numbers, and arrays. The following literals
exist:

* ``"Hello World"``: Everything between two double or single quotes is a
  string. They are useful whenever you need a string in the template (for
  example as arguments to function calls, filters or just to extend or include
  a template). A string can contain a delimiter if it is preceded by a
  backslash (``\``) -- like in ``'It\'s good'``. If the string contains a
  backslash (e.g. ``'c:\Program Files'``) escape it by doubling it
  (e.g. ``'c:\\Program Files'``).

* ``42`` / ``42.23``: Integers and floating point numbers are created by
  writing the number down. If a dot is present the number is a float,
  otherwise an integer.

* ``["foo", "bar"]``: Arrays are defined by a sequence of expressions
  separated by a comma (``,``) and wrapped with squared brackets (``[]``).

* ``{"foo": "bar"}``: Hashes are defined by a list of keys and values
  separated by a comma (``,``) and wrapped with curly braces (``{}``):

  .. code-block:: twig

    {# keys as string #}
    { 'foo': 'foo', 'bar': 'bar' }

    {# keys as names (equivalent to the previous hash) #}
    { foo: 'foo', bar: 'bar' }

    {# keys as integer #}
    { 2: 'foo', 4: 'bar' }

    {# keys as expressions (the expression must be enclosed into parentheses) #}
    {% set foo = 'foo' %}
    { (foo): 'foo', (1 + 1): 'bar', (foo ~ 'b'): 'baz' }

* ``true`` / ``false``: ``true`` represents the true value, ``false``
  represents the false value.

* ``null``: ``null`` represents no specific value. This is the value returned
  when a variable does not exist. ``none`` is an alias for ``null``.

Arrays and hashes can be nested:

.. code-block:: twig

    {% set foo = [1, {"foo": "bar"}] %}

.. tip::

    Using double-quoted or single-quoted strings has no impact on performance
    but :ref:`string interpolation <templates-string-interpolation>` is only
    supported in double-quoted strings.

Math
~~~~

Twig allows you to do math in templates; the following operators are supported:

* ``+``: Adds two numbers together (the operands are casted to numbers). ``{{
  1 + 1 }}`` is ``2``.

* ``-``: Subtracts the second number from the first one. ``{{ 3 - 2 }}`` is
  ``1``.

* ``/``: Divides two numbers. The returned value will be a floating point
  number. ``{{ 1 / 2 }}`` is ``{{ 0.5 }}``.

* ``%``: Calculates the remainder of an integer division. ``{{ 11 % 7 }}`` is
  ``4``.

* ``//``: Divides two numbers and returns the floored integer result. ``{{ 20
  // 7 }}`` is ``2``, ``{{ -20  // 7 }}`` is ``-3`` (this is just syntactic
  sugar for the :doc:`round<filters/round>` filter).

* ``*``: Multiplies the left operand with the right one. ``{{ 2 * 2 }}`` would
  return ``4``.

* ``**``: Raises the left operand to the power of the right operand. ``{{ 2 **
  3 }}`` would return ``8``.

.. _template_logic:

Logic
~~~~~

You can combine multiple expressions with the following operators:

* ``and``: Returns true if the left and the right operands are both true.

* ``or``: Returns true if the left or the right operand is true.

* ``not``: Negates a statement.

* ``(expr)``: Groups an expression.

.. note::

    Twig also supports bitwise operators (``b-and``, ``b-xor``, and ``b-or``).

.. note::

    Operators are case sensitive.

Comparisons
~~~~~~~~~~~

The following comparison operators are supported in any expression: ``==``,
``!=``, ``<``, ``>``, ``>=``, and ``<=``.

You can also check if a string ``starts with`` or ``ends with`` another
string:

.. code-block:: twig

    {% if 'Fabien' starts with 'F' %}
    {% endif %}

    {% if 'Fabien' ends with 'n' %}
    {% endif %}

.. note::

    For complex string comparisons, the ``matches`` operator allows you to use
    `regular expressions`_:

    .. code-block:: twig

        {% if phone matches '/^[\\d\\.]+$/' %}
        {% endif %}

Containment Operator
~~~~~~~~~~~~~~~~~~~~

The ``in`` operator performs containment test. It returns ``true`` if the left
operand is contained in the right:

.. code-block:: twig

    {# returns true #}

    {{ 1 in [1, 2, 3] }}

    {{ 'cd' in 'abcde' }}

.. tip::

    You can use this filter to perform a containment test on strings, arrays,
    or objects implementing the ``Traversable`` interface.

To perform a negative test, use the ``not in`` operator:

.. code-block:: twig

    {% if 1 not in [1, 2, 3] %}

    {# is equivalent to #}
    {% if not (1 in [1, 2, 3]) %}

Test Operator
~~~~~~~~~~~~~

The ``is`` operator performs tests. Tests can be used to test a variable against
a common expression. The right operand is name of the test:

.. code-block:: twig

    {# find out if a variable is odd #}

    {{ name is odd }}

Tests can accept arguments too:

.. code-block:: twig

    {% if post.status is constant('Post::PUBLISHED') %}

Tests can be negated by using the ``is not`` operator:

.. code-block:: twig

    {% if post.status is not constant('Post::PUBLISHED') %}

    {# is equivalent to #}
    {% if not (post.status is constant('Post::PUBLISHED')) %}

Go to the :doc:`tests<tests/index>` page to learn more about the built-in
tests.

Other Operators
~~~~~~~~~~~~~~~

The following operators don't fit into any of the other categories:

* ``|``: Applies a filter.

* ``..``: Creates a sequence based on the operand before and after the operator
  (this is syntactic sugar for the :doc:`range<functions/range>` function):

  .. code-block:: twig

      {{ 1..5 }}

      {# equivalent to #}
      {{ range(1, 5) }}

  Note that you must use parentheses when combining it with the filter operator
  due to the :ref:`operator precedence rules <twig-expressions>`:

  .. code-block:: twig

      (1..5)|join(', ')

* ``~``: Converts all operands into strings and concatenates them. ``{{ "Hello
  " ~ name ~ "!" }}`` would return (assuming ``name`` is ``'John'``) ``Hello
  John!``.

* ``.``, ``[]``: Gets an attribute of a variable.

* ``?:``: The ternary operator:

  .. code-block:: twig

      {{ foo ? 'yes' : 'no' }}
      {{ foo ?: 'no' }} is the same as {{ foo ? foo : 'no' }}
      {{ foo ? 'yes' }} is the same as {{ foo ? 'yes' : '' }}

* ``??``: The null-coalescing operator:

  .. code-block:: twig

      {# returns the value of foo if it is defined and not null, 'no' otherwise #}
      {{ foo ?? 'no' }}

.. _templates-string-interpolation:

String Interpolation
~~~~~~~~~~~~~~~~~~~~

String interpolation (``#{expression}``) allows any valid expression to appear
within a *double-quoted string*. The result of evaluating that expression is
inserted into the string:

.. code-block:: twig

    {{ "foo #{bar} baz" }}
    {{ "foo #{1 + 2} baz" }}

.. _templates-whitespace-control:

Whitespace Control
------------------

The first newline after a template tag is removed automatically (like in PHP).
Whitespace is not further modified by the template engine, so each whitespace
(spaces, tabs, newlines etc.) is returned unchanged.

You can also control whitespace on a per tag level. By using the whitespace
control modifiers on your tags, you can trim leading and or trailing whitespace.

Twig supports two modifiers:

* *Whitespace trimming* via the ``-`` modifier: Removes all whitespace
  (including newlines);

* *Line whitespace trimming* via the ``~`` modifier: Removes all whitespace
  (excluding newlines). Using this modifier on the right disables the default
  removal of the first newline inherited from PHP.

The modifiers can be used on either side of the tags like in ``{%-`` or ``-%}``
and they consume all whitespace for that side of the tag. It is possible to use
the modifiers on one side of a tag or on both sides:

.. code-block:: twig

    {% set value = 'no spaces' %}
    {#- No leading/trailing whitespace -#}
    {%- if true -%}
        {{- value -}}
    {%- endif -%}
    {# output 'no spaces' #}

    <li>
        {{ value }}    </li>
    {# outputs '<li>\n    no spaces    </li>' #}

    <li>
        {{- value }}    </li>
    {# outputs '<li>no spaces    </li>' #}

    <li>
        {{~ value }}    </li>
    {# outputs '<li>\nno spaces    </li>' #}

.. tip::

    In addition to the whitespace modifiers, Twig also has a ``spaceless`` filter
    that removes whitespace **between HTML tags**:

    .. code-block:: twig

        {% apply spaceless %}
            <div>
                <strong>foo bar</strong>
            </div>
        {% endapply %}

        {# output will be <div><strong>foo bar</strong></div> #}

Extensions
----------

Twig can be extended. If you want to create your own extensions, read the
:ref:`Creating an Extension <creating_extensions>` chapter.

.. _`Twig bundle`:                https://github.com/Anomareh/PHP-Twig.tmbundle
.. _`Jinja syntax plugin`:        http://jinja.pocoo.org/docs/integration/#vim
.. _`vim-twig plugin`:            https://github.com/lumiliet/vim-twig
.. _`Twig syntax plugin`:         http://plugins.netbeans.org/plugin/37069/php-twig
.. _`Twig plugin`:                https://github.com/pulse00/Twig-Eclipse-Plugin
.. _`Twig language definition`:   https://github.com/gabrielcorpse/gedit-twig-template-language
.. _`Twig syntax mode`:           https://github.com/bobthecow/Twig-HTML.mode
.. _`other Twig syntax mode`:     https://github.com/muxx/Twig-HTML.mode
.. _`Notepad++ Twig Highlighter`: https://github.com/Banane9/notepadplusplus-twig
.. _`web-mode.el`:                http://web-mode.org/
.. _`regular expressions`:        https://secure.php.net/manual/en/pcre.pattern.php
.. _`PHP-twig for atom`:          https://github.com/reesef/php-twig
.. _`TwigFiddle`:                 https://twigfiddle.com/
.. _`Twig pack`:                  https://marketplace.visualstudio.com/items?itemName=bajdzis.vscode-twig-pack
