Sections

Volt: Template Engine


Overview

Volt is an ultra-fast and designer friendly templating language written in C for PHP. It provides you a set of helpers to write views in an easy way. Volt is highly integrated with other components of Phalcon, just as you can use it as a stand-alone component in your applications.

Volt is inspired by Jinja, originally created by Armin Ronacher. Therefore many developers will be in familiar territory using the same syntax they have been using with similar template engines. Volt’s syntax and features have been enhanced with more elements and of course with the performance that developers have been accustomed to while working with Phalcon.

Introduction

Volt views are compiled to pure PHP code, so basically they save the effort of writing PHP code manually:

{# app/views/products/show.volt #}

{% block last_products %}

{% for product in products %}
    * Name: {{ product.name|e }}
    {% if product.status === 'Active' %}
       Price: {{ product.price + product.taxes/100 }}
    {% endif  %}
{% endfor  %}

{% endblock %}

Activating Volt

As with other templating engines, you may register Volt in the view component, using a new extension or reusing the standard .phtml:

<?php

use Phalcon\Mvc\View;
use Phalcon\Mvc\View\Engine\Volt;

// Register Volt as a service
$di->set(
    'voltService',
    function ($view, $di) {
        $volt = new Volt($view, $di);

        $volt->setOptions(
            [
                'path'      => '../app/compiled-templates/',
                'extension' => '.compiled',
            ]
        );

        return $volt;
    }
);

// Register Volt as template engine
$di->set(
    'view',
    function () {
        $view = new View();

        $view->setViewsDir('../app/views/');

        $view->registerEngines(
            [
                '.volt' => 'voltService',
            ]
        );

        return $view;
    }
);

Use the standard .phtml extension:

<?php

$view->registerEngines(
    [
        '.phtml' => 'voltService',
    ]
);

You don’t have to specify the Volt Service in the DI; you can also use the Volt engine with the default settings:

<?php

$view->registerEngines(
    [
        '.volt' => Phalcon\Mvc\View\Engine\Volt::class,
    ]
);

If you do not want to reuse Volt as a service, you can pass an anonymous function to register the engine instead of a service name:

<?php

use Phalcon\Mvc\View;
use Phalcon\Mvc\View\Engine\Volt;

// Registrar Volt como motor de plantillas con una función anónima
$di->set(
    'view',
    function () {
        $view = new View();

        $view->setViewsDir('../app/views/');

        $view->registerEngines(
            [
                '.volt' => function ($view, $di) {
                    $volt = new Volt($view, $di);

                    // Configurar otras opciones aquí

                    return $volt;
                }
            ]
        );

        return $view;
    }
);

The following options are available in Volt:

Opción Descripción Predeterminado
autoescape Enables globally autoescape of HTML false
always Tell Volt if the templates must be compiled in each request or only when they change false
extension An additional extension appended to the compiled PHP file .php
path A writeable path where the compiled PHP templates will be placed ./
separator Volt replaces the directory separators / and \ by this separator in order to create a single file in the compiled directory %%
prefix Permite anteponer un prefijo a las plantillas en la ruta de compilación null
stat Whether Phalcon must check if exists differences between the template file and its compiled path true

The compilation path is generated according to the above options, if the developer wants total freedom defining the compilation path, an anonymous function can be used to generate it, this function receives the relative path to the template in the views directory. The following examples show how to change the compilation path dynamically:

<?php

// Just append the .php extension to the template path
// leaving the compiled templates in the same directory
$volt->setOptions(
    [
        'path' => function ($templatePath) {
            return $templatePath . '.php';
        }
    ]
);

// Recursively create the same structure in another directory
$volt->setOptions(
    [
        'path' => function ($templatePath) {
            $dirName = dirname($templatePath);

            if (!is_dir('cache/' . $dirName)) {
                mkdir('cache/' . $dirName , 0777 , true);
            }

            return 'cache/' . $dirName . '/'. $templatePath . '.php';
        }
    ]
);

Basic Usage

A view consists of Volt code, PHP and HTML. A set of special delimiters is available to enter into Volt mode. ` {% … %} ` is used to execute statements such as for-loops or assign values and ` {{ … }}`, prints the result of an expression to the template.

Below is a minimal template that illustrates a few basics:

{# app/views/posts/show.phtml #}
<!DOCTYPE html>
<html>
    <head>
        <title>{{ title }} - An example blog</title>
    </head>
    <body>

        {% if show_navigation %}
            <ul id='navigation'>
                {% for item in menu %}
                    <li>
                        <a href='{{ item.href }}'>
                            {{ item.caption }}
                        </a>
                    </li>
                {% endfor %}
            </ul>
        {% endif %}

        <h1>{{ post.title }}</h1>

        <div class='content'>
            {{ post.content }}
        </div>

    </body>
</html>```

Using [Phalcon\Mvc\View](api/Phalcon_Mvc_View) you can pass variables from the controller to the views. In the above example, four variables were passed to the view: `show_navigation`, `menu`, `title` and `post`:

```php
<?php

use Phalcon\Mvc\Controller;

class PostsController extends Controller
{
    public function showAction()
    {
        $post = Post::findFirst();
        $menu = Menu::findFirst();

        $this->view->show_navigation = true;
        $this->view->menu            = $menu;
        $this->view->title           = $post->title;
        $this->view->post            = $post;

        // O...

        $this->view->setVar('show_navigation', true);
        $this->view->setVar('menu',            $menu);
        $this->view->setVar('title',           $post->title);
        $this->view->setVar('post',            $post);
    }
}

Variables

Object variables may have attributes which can be accessed using the syntax: foo.bar. If you are passing arrays, you have to use the square bracket syntax: foo['bar']

{{ post.title }} {# for $post->title #}
{{ post['title'] }} {# for $post['title'] #}

Filters

Variables can be formatted or modified using filters. The pipe operator | is used to apply filters to variables:

{{ post.title|e }}
{{ post.content|striptags }}
{{ name|capitalize|trim }}

The following is the list of available built-in filters in Volt:

Filtro Descripción
abs Applies the abs PHP function to a value.
capitalize Capitalizes a string by applying the ucwords PHP function to the value
convert_encoding Convierte una cadena de un conjunto de caracteres a otro
default Establece un valor predeterminado en caso de que la expresión evaluada este vacía (no se establece o se evalúa como un valor falso)
e Se aplica Phalcon\Escaper->escapeHtml() al valor
escape Se aplica Phalcon\Escaper->escapeHtml() al valor
escape_attr Se aplica Phalcon\Escaper->escapeHtmlAttr() al valor
escape_css Se aplica Phalcon\Escaper->escapeCss() al valor
escape_js Se aplica Phalcon\Escaper->escapeJs() al valor
format Formats a string using sprintf.
json_encode Converts a value into its JSON representation
json_decode Converts a value from its JSON representation to a PHP representation
join Joins the array parts using a separator join
keys Returns the array keys using array_keys
left_trim Applies the ltrim PHP function to the value. Removing extra spaces
length Cuenta la longitud de la cadena de texto o cuántos elementos hay en un array u objeto
lower Cambiar una cadena a minúsculas
nl2br Changes newlines \n by line breaks (<br />). Uses the PHP function nl2br
right_trim Applies the rtrim PHP function to the value. Removing extra spaces
sort Sorts an array using the PHP function asort
stripslashes Applies the stripslashes PHP function to the value. Removing escaped quotes
striptags Applies the striptags PHP function to the value. Removing HTML tags
trim Applies the trim PHP function to the value. Removing extra spaces
upper Change the case of a string to uppercase
url_encode Applies the urlencode PHP function to the value

Examples:

{# e or escape filter #}
{{ '<h1>Hello<h1>'|e }}
{{ '<h1>Hello<h1>'|escape }}

{# trim filter #}
{{ '   hello   '|trim }}

{# striptags filter #}
{{ '<h1>Hello<h1>'|striptags }}

{# slashes filter #}
{{ ''this is a string''|slashes }}

{# stripslashes filter #}
{{ '\'this is a string\''|stripslashes }}

{# capitalize filter #}
{{ 'hello'|capitalize }}

{# lower filter #}
{{ 'HELLO'|lower }}

{# upper filter #}
{{ 'hello'|upper }}

{# length filter #}
{{ 'robots'|length }}
{{ [1, 2, 3]|length }}

{# nl2br filter #}
{{ 'some\ntext'|nl2br }}

{# sort filter #}
{% set sorted = [3, 1, 2]|sort %}

{# keys filter #}
{% set keys = ['first': 1, 'second': 2, 'third': 3]|keys %}

{# join filter #}
{% set joined = 'a'..'z'|join(',') %}

{# format filter #}
{{ 'My real name is %s'|format(name) }}

{# json_encode filter #}
{% set encoded = robots|json_encode %}

{# json_decode filter #}
{% set decoded = '{'one':1,'two':2,'three':3}'|json_decode %}

{# url_encode filter #}
{{ post.permanent_link|url_encode }}

{# convert_encoding filter #}
{{ 'désolé'|convert_encoding('utf8', 'latin1') }}

Comments

Comments may also be added to a template using the ` {# … #}` delimiters. All text inside them is just ignored in the final output:

{# note: this is a comment
    {% set price = 100; %}
#}```

## List of Control Structures

Volt provides a set of basic but powerful control structures for use in templates:

### For

Loop over each item in a sequence. The following example shows how to traverse a set of 'robots' and print his/her name:

```twig
<h1>Robots</h1>
<ul>
    {% for robot in robots %}
        <li>
            {{ robot.name|e }}
        </li>
    {% endfor %}
</ul>```

for-loops can also be nested:

```twig
<h1>Robots</h1>
{% for robot in robots %}
    {% for part in robot.parts %}
        Robot: {{ robot.name|e }}

Part: {{ part.name|e }} <br />
    {% endfor %}
{% endfor %}

You can get the element keys as in the PHP counterpart using the following syntax:

{% set numbers = ['one': 1, 'two': 2, 'three': 3] %}

{% for name, value in numbers %}
    Name: {{ name }} Value: {{ value }}
{% endfor %}

An if evaluation can be optionally set:

{% set numbers = ['one': 1, 'two': 2, 'three': 3] %}

{% for value in numbers if value < 2 %}
    Value: {{ value }}
{% endfor %}

{% for name, value in numbers if name !== 'two' %}
    Name: {{ name }} Value: {{ value }}
{% endfor %}

If an else is defined inside the for, it will be executed if the expression in the iterator result in zero iterations:

<h1>Robots</h1>
{% for robot in robots %}
    Robot: {{ robot.name|e }} Part: {{ part.name|e }} <br />
{% else %}
    There are no robots to show
{% endfor %}

Alternative syntax:

<h1>Robots</h1>
{% for robot in robots %}
    Robot: {{ robot.name|e }} Part: {{ part.name|e }} <br />
{% elsefor %}
    There are no robots to show
{% endfor %}

Loop Controls

The break and continue statements can be used to exit from a loop or force an iteration in the current block:

{# skip the even robots #}
{% for index, robot in robots %}
    {% if index is even %}
        {% continue %}
    {% endif %}
    ...
{% endfor %}

{# exit the foreach on the first even robot #}
{% for index, robot in robots %}
    {% if index is even %}
        {% break %}
    {% endif %}
    ...
{% endfor %}

If

As PHP, an if statement checks if an expression is evaluated as true or false:

<h1>Cyborg Robots</h1>
<ul>
    {% for robot in robots %}
        {% if robot.type === 'cyborg' %}
            <li>{{ robot.name|e }}</li>
        {% endif %}
    {% endfor %}
</ul>```

The else clause is also supported:

```twig
<h1>Robots</h1>
<ul>
    {% for robot in robots %}
        {% if robot.type === 'cyborg' %}
            <li>{{ robot.name|e }}</li>
        {% else %}
            <li>{{ robot.name|e }} (not a cyborg)</li>
        {% endif %}
    {% endfor %}
</ul>```

The `elseif` control flow structure can be used together with if to emulate a `switch` block:

```twig
{% if robot.type === 'cyborg' %}
    Robot is a cyborg
{% elseif robot.type === 'virtual' %}
    Robot is virtual
{% elseif robot.type === 'mechanical' %}
    Robot is mechanical
{% endif %}

Switch

An alternative to the if statement is switch, allowing you to create logical execution paths in your application:

{% switch foo %}
    {% case 0 %}
    {% case 1 %}
    {% case 2 %}
        "foo" is less than 3 but not negative
        {% break %}
    {% case 3 %}
        "foo" is 3
        {% break %}
    {% default %}
        "foo" is {{ foo }}
{% endswitch %}

The switch statement executes statement by statement, therefore the break statement is necessary in some cases. Any output (including whitespace) between a switch statement and the first case will result in a syntax error. Empty lines and whitespaces can therefore be cleared to reduce the number of errors see here.

case sin switch

{% case EXPRESSION %}

Will throw Fatal error: Uncaught Phalcon\Mvc\View\Exception: Unexpected CASE.

switch sin endswitch

{% switch EXPRESSION %}
Will throw `Fatal error: Uncaught Phalcon\Mvc\View\Exception: Syntax error, unexpected EOF in ..., there is a 'switch' block without 'endswitch'`.

default sin switch

{% default %}

Will not throw an error because default is a reserved word for filters like ` {{ EXPRESSION | default(VALUE) }}` but in this case the expression will only output an empty char ‘’ .

switch anidados

{% switch EXPRESSION %}
  {% switch EXPRESSION %}
  {% endswitch %}
{% endswitch %}

Will throw Fatal error: Uncaught Phalcon\Mvc\View\Exception: A nested switch detected. There is no nested switch-case statements support in ... on line ...

un switch sin expresión

{% switch %}
  {% case EXPRESSION %}
      {% break %}
{% endswitch %}

Will throw Fatal error: Uncaught Phalcon\Mvc\View\Exception: Syntax error, unexpected token %}in ... on line ...

Loop Context

A special variable is available inside for loops providing you information about

Variable Descripción
loop.index The current iteration of the loop. (1 indexed)
loop.index0 The current iteration of the loop. (0 indexed)
loop.revindex El número de iteraciones desde el final del bucle (comenzando desde 1)
loop.revindex0 El número de iteraciones desde el final del bucle (comenzando desde 0)
loop.first Si es la primera iteración, el valor será true.
loop.last Si es la última iteración, el valor será true.
loop.length El número de elementos iterar

Example:

{% for robot in robots %}
    {% if loop.first %}
        <table>
            <tr>
                <th>#</th>
                <th>Id</th>
                <th>Name</th>
            </tr>
    {% endif %}
            <tr>
                <td>{{ loop.index }}</td>
                <td>{{ robot.id }}</td>
                <td> {{ robot.name }}
    </td>
            </tr>
    {% if loop.last %}
        </table>
    {% endif %}
{% endfor %}

Assignments

Variables may be changed in a template using the instruction set:

{% set fruits = ['Apple', 'Banana', 'Orange'] %}

{% set name = robot.name %}

Multiple assignments are allowed in the same instruction:

{% set fruits = ['Apple', 'Banana', 'Orange'], name = robot.name, active = true %}

Additionally, you can use compound assignment operators:

{% set price += 100.00 %}

{% set age *= 5 %}

The following operators are available:

Operator Descripción
= Asignación estándar
+= Asignación de adición
-= Asignación de resta
\*= Asignación de multiplicación
/= Asignación de división

Expressions

Volt provides a basic set of expression support, including literals and common operators. A expression can be evaluated and printed using the ` {{ and }}` delimiters:

{{ (1 + 1) * 2 }}

If an expression needs to be evaluated without be printed the do statement can be used:

{% do (1 + 1) * 2 %}

Literals

The following literals are supported:

Filtro Descripción
'esto es una cadena' Los textos entre doble comillas simples o dobles se tratan como cadenas de caracteres
100.25 Los números con parte decimal se tratan como dobles/flotadores
100 Los número sin parte decimal se tratan como enteros
false La constante ‘false’ es el valor booleano falso
true La constante ‘true’ es el valor booleano verdadero
null La constante ‘null’ es el valor Null

Arrays

You can create arrays by enclosing a list of values in square brackets:

{# Simple array #}
{{ ['Apple', 'Banana', 'Orange'] }}

{# Other simple array #}
{{ ['Apple', 1, 2.5, false, null] }}

{# Multi-Dimensional array #}
{{ [[1, 2], [3, 4], [5, 6]] }}

{# Hash-style array #}
{{ ['first': 1, 'second': 4/2, 'third': '3'] }}

Curly braces also can be used to define arrays or hashes:

{% set myArray = {'Apple', 'Banana', 'Orange'} %}
{% set myHash  = {'first': 1, 'second': 4/2, 'third': '3'} %}

Math

You may make calculations in templates using the following operators:

| Operator | Descripción | |:——–:| ———————————————————————————————- | | + | Perform an adding operation. ` {{ 2 + 3 }} returns 5 | | - | Perform a substraction operation {{ 2 - 3 }} returns -1 | | * | Perform a multiplication operation {{ 2 * 3 }} ` returns 6 | | / | Perform a division operation ` {{ 10 / 2 }} ` returns 5 | | % | Calculate the remainder of an integer division ` {{ 10 % 3 }} ` returns 1 |

Comparisons

The following comparison operators are available:

Operator Descripción
== Comprobar si ambos operandos son iguales
!= Comprobar si ambos operandos no son iguales
<> Comprobar si ambos operandos no son iguales
> Compruebe si el operando izquierdo es mayor que el operando derecho
< Compruebe si el operando izquierdo es menor que el operando derecho
<= Compruebe si el operando de la izquierda es menor o igual que el operando derecho
>= Compruebe si el operando izquierdo es mayor o igual que el operando derecho
=== Compruebe si ambos operandos son idénticos
!== Comprobar si ambos operandos no son identicos

Logic

Logic operators are useful in the if expression evaluation to combine multiple tests:

Operator Descripción
o Devuelve true si el operando de la derecha o la izquierda se evalúa como true
and Devuelve true si los operandos izquierdo y derecho se evalúan como verdadero
not Niega una expresión
( expr ) Las expresiones se agrupan entre paréntesis

Other Operators

Additional operators seen the following operators are available:

| Operator | Descripción | | —————– | ————————————————————————————————– | | ~ | Concatenates both operands ` {{ ‘hello ‘ ~ ‘world’ }} ` | | | | Applies a filter in the right operand to the left ` {{ ‘hello’|uppercase }} | | .. | Creates a range {{ ‘a’..’z’ }} ` ` {{ 1..10 }} | | is | Alias de == (igual), también realiza pruebas | | in | Para comprobar si una expresión está contenida en otras expresiones if ‘a’ in ‘abc’ | | is not | Alias de != (no iguales) | | ‘a’ ? ‘b’ : ‘c’ | Ternary operator. The same as the PHP ternary operator | | ++ | Incrementa un valor | | –` | Decrementa un valor |

The following example shows how to use operators:

{% set robots = ['Voltron', 'Astro Boy', 'Terminator', 'C3PO'] %}

{% for index in 0..robots|length %}
    {% if robots[index] is defined %}
        {{ 'Name: ' ~ robots[index] }}
    {% endif %}
{% endfor %}

Tests

Tests can be used to test if a variable has a valid expected value. The operator is is used to perform the tests:

{% set robots = ['1': 'Voltron', '2': 'Astro Boy', '3': 'Terminator', '4': 'C3PO'] %}

{% for position, name in robots %}
    {% if position is odd %}
        {{ name }}
    {% endif %}
{% endfor %}

The following built-in tests are available in Volt:

Prueba Descripción
defined Comprueba si una variable esta definida (isset())
divisibleby Comprueba si un valor es divisible por otro valor
empty Comprueba si una variable está vacía
even Comprueba si un valor numérico es par
iterable Checks if a value is iterable. Can be traversed by a ‘for’ statement
numeric Comprueba si el valor es numérico
odd Comprueba si un valor numérico es impar
sameas Comprueba si un valor es idéntico a otro valor
scalar Comprueba si el valor es escalar (no una matriz, objeto o recurso)
type Comprueba si un valor es del tipo especificado

More examples:

{% if robot is defined %}
    The robot variable is defined
{% endif %}

{% if robot is empty %}
    The robot is null or isn't defined
{% endif %}

{% for key, name in [1: 'Voltron', 2: 'Astroy Boy', 3: 'Bender'] %}
    {% if key is even %}
        {{ name }}
    {% endif %}
{% endfor %}

{% for key, name in [1: 'Voltron', 2: 'Astroy Boy', 3: 'Bender'] %}
    {% if key is odd %}
        {{ name }}
    {% endif %}
{% endfor %}

{% for key, name in [1: 'Voltron', 2: 'Astroy Boy', 'third': 'Bender'] %}
    {% if key is numeric %}
        {{ name }}
    {% endif %}
{% endfor %}

{% set robots = [1: 'Voltron', 2: 'Astroy Boy'] %}
{% if robots is iterable %}
    {% for robot in robots %}
        ...
    {% endfor %}
{% endif %}

{% set world = 'hello' %}
{% if world is sameas('hello') %}
    {{ 'it's hello' }}
{% endif %}

{% set external = false %}
{% if external is type('boolean') %}
    {{ 'external is false or true' }}
{% endif %}

Macros

Macros can be used to reuse logic in a template, they act as PHP functions, can receive parameters and return values:

{# Macro 'display a list of links to related topics' #}
{%- macro related_bar(related_links) %}
    <ul>
        {%- for link in related_links %}
            <li>
                <a href='{{ url(link.url) }}' title='{{ link.title|striptags }}'>
                    {{ link.text }}
                </a>
            </li>
        {%- endfor %}
    </ul>
{%- endmacro %}

{# Print related links #}
{{ related_bar(links) }}

<div>This is the content</div>

{# Print related links again #}
{{ related_bar(links) }}

When calling macros, parameters can be passed by name:

{%- macro error_messages(message, field, type) %}
    <div>
        <span class='error-type'>{{ type }}</span>
        <span class='error-field'>{{ field }}</span>
        <span class='error-message'>{{ message }}</span>
    </div>
{%- endmacro %}

{# Call the macro #}
{{ error_messages('type': 'Invalid', 'message': 'The name is invalid', 'field': 'name') }}

Macros can return values:

{%- macro my_input(name, class) %}
    {% return text_field(name, 'class': class) %}
{%- endmacro %}

{# Call the macro #}
{{ '<p>' ~ my_input('name', 'input-text') ~ '</p>' }}

And receive optional parameters:

```twig{%- macro my_input(name, class=’input-text’) %} {% return text_field(name, ‘class’: class) %} {%- endmacro %}

{# Call the macro #} {{ ‘<p>’ ~ my_input(‘name’) ~ ‘</p>’ }} {{ ‘<p>’ ~ my_input(‘name’, ‘input-text’) ~ ‘</p>’ }}


## Using Tag Helpers

Volt is highly integrated with [Phalcon\Tag](api/Phalcon_Tag), so it's easy to use the helpers provided by that component in a Volt template:

```twig{{ javascript_include('js/jquery.js') }}

{{ form('products/save', 'method': 'post') }}

    <label for='name'>Name</label>
    {{ text_field('name', 'size': 32) }}

    <label for='type'>Type</label>
    {{ select('type', productTypes, 'using': ['id', 'name']) }}

    {{ submit_button('Send') }}

{{ end_form() }}

The following PHP is generated:

<?php echo Phalcon\Tag::javascriptInclude('js/jquery.js') ?>

<?php echo Phalcon\Tag::form(array('products/save', 'method' => 'post')); ?>

    <label for='name'>Name</label>
    <?php echo Phalcon\Tag::textField(array('name', 'size' => 32)); ?>

    <label for='type'>Type</label>
    <?php echo Phalcon\Tag::select(array('type', $productTypes, 'using' => array('id', 'name'))); ?>

    <?php echo Phalcon\Tag::submitButton('Send'); ?>{{ end_form() }}

To call a Phalcon\Tag helper, you only need to call an uncamelized version of the method:

Método Función en Volt
Phalcon\Tag::checkField check_field
Phalcon\Tag::dateField date_field
Phalcon\Tag::emailField email_field
Phalcon\Tag::endForm end_form
Phalcon\Tag::fileField file_field
Phalcon\Tag::form form
Phalcon\Tag::friendlyTitle friendly_title
Phalcon\Tag::getTitle get_title
Phalcon\Tag::hiddenField hidden_field
Phalcon\Tag::image image
Phalcon\Tag::javascriptInclude javascript_include
Phalcon\Tag::linkTo link_to
Phalcon\Tag::numericField numeric_field
Phalcon\Tag::passwordField password_field
Phalcon\Tag::radioField radio_field
Phalcon\Tag::select select
Phalcon\Tag::selectStatic select_static
Phalcon\Tag::stylesheetLink stylesheet_link
Phalcon\Tag::submitButton submit_button
Phalcon\Tag::textArea text_area
Phalcon\Tag::textField text_field

Functions

The following built-in functions are available in Volt:

Nombre Descripción
content Incluye el contenido producido en una etapa anterior de renderizado
get_content Alias de content
partial Carga dinámicamente una vista parcial en la plantilla actual
super Presenta el contenido del bloque padre
time Llama a la función time() de PHP
date Llama a la función time() de PHP
dump Llama la función var_dump() de PHP
version Devuelve la versión actual del framework
constant Lee una constante de PHP
url Genera una dirección URL utilizando el servicio ‘url’

View Integration

Also, Volt is integrated with Phalcon\Mvc\View, you can play with the view hierarchy and include partials as well:

```twig{{ content() }}


A partial is included in runtime, Volt also provides `include`, this compiles the content of a view and returns its contents as part of the view which was included:

```twig{# Simple include of a partial #}
<div id='footer'>
    {% include 'partials/footer' %}
</div>

{# Passing extra variables #}
<div id='footer'>
    {% include 'partials/footer' with ['links': links] %}
</div>

Include

include has a special behavior that will help us improve performance a bit when using Volt, if you specify the extension when including the file and it exists when the template is compiled, Volt can inline the contents of the template in the parent template where it’s included. Templates aren’t inlined if the include have variables passed with with:

```twig{# The contents of ‘partials/footer.volt’ is compiled and inlined #}


### Partial vs Include

Keep the following points in mind when choosing to use the `partial` function or `include`:

| Tipo      | Descripción                                                                                                   |
| --------- | ------------------------------------------------------------------------------------------------------------- |
| `partial` | Permite incluir plantillas en Volt, igual que en otros motores de plantillas                                  |
|           | Permite pasar de una expresión como una variable permitiendo incluir el contenido de otra vista dinámicamente |
|           | Es mejor si el contenido que usted tiene que incluir cambia con frecuencia                                    |
| `include` | Copia el contenido compilado en la vista, mejorando el rendimiento                                            |
|           | Sólo permite incluir plantillas creadas con Volt                                                              |
|           | Requiere de una plantilla existente en tiempo de compilación                                                  |

## Template Inheritance

With template inheritance you can create base templates that can be extended by others templates allowing to reuse code. A base template define *blocks* than can be overridden by a child template. Let's pretend that we have the following base template:

```twig{# templates/base.volt #}
<!DOCTYPE html>
<html>
    <head>
        {% block head %}
            <link rel='stylesheet' href='style.css' />
        {% endblock %}

        <title>{% block title %}
{% endblock %}
- My Webpage</title>
    </head>

    <body>
        <div id='content'>{% block content %}
    

{% endblock %}
</div>

        <div id='footer'>
            {% block footer %}&copy; Copyright 2015, All rights reserved.{% endblock %}
        </div>
    </body>
</html>

From other template we could extend the base template replacing the blocks:

```twig{% extends ‘templates/base.volt’ %}

{% block title %}Index{% endblock %}

{% block head %}{% endblock %}

{% block content %}

<h1>Index</h1>
<p class='important'>Welcome on my awesome homepage.</p>

{% endblock %}


Not all blocks must be replaced at a child template, only those that are needed. The final output produced will be the following:

```html
<!DOCTYPE html>
<html>
    <head>
        <style type='text/css'>.important { color: #336699; }</style>

        <title>Index - My Webpage</title>
    </head>

    <body>
        <div id='content'>
            <h1>Index</h1>
            <p class='important'>Welcome on my awesome homepage.</p>
        </div>

        <div id='footer'>
            &copy; Copyright 2015, All rights reserved.
        </div>
    </body>
</html>

Multiple Inheritance

Extended templates can extend other templates. The following example illustrates this:

```twig{# main.volt #} <!DOCTYPE html>

Title {% block content %}{% endblock %}

Template `layout.volt` extends `main.volt`

```twig{# layout.volt #}
{% extends 'main.volt' %}

{% block content %}

    <h1>Table of contents</h1>

{% endblock %}

Finally a view that extends layout.volt:

```twig{# index.volt #} {% extends ‘layout.volt’ %}

{% block content %}{{ super() }}

<ul>
    <li>Some option</li>
    <li>Some other option</li>
</ul>

{% endblock %}


Rendering `index.volt` produces:

```html
<!DOCTYPE html>
<html>
    <head>
        <title>Title</title>
    </head>

    <body>

        <h1>Table of contents</h1>

        <ul>
            <li>Some option</li>
            <li>Some other option</li>
        </ul>

    </body>
</html>

Note the call to the function super(). With that function it’s possible to render the contents of the parent block. As partials, the path set to extends is a relative path under the current views directory (i.e. app/views/).

By default, and for performance reasons, Volt only checks for changes in the children templates to know when to re-compile to plain PHP again, so it is recommended initialize Volt with the option 'always' => true. Thus, the templates are compiled always taking into account changes in the parent templates.

Autoescape mode

You can enable auto-escaping of all variables printed in a block using the autoescape mode:

Manually escaped: {{ robot.name|e }}{% autoescape true %}
    Autoescaped: {{ robot.name }}
    {% autoescape false %}
        No Autoescaped: {{ robot.name }}{% endautoescape %}
{% endautoescape %}

Extending Volt

Unlike other template engines, Volt itself is not required to run the compiled templates. Once the templates are compiled there is no dependence on Volt. With performance independence in mind, Volt only acts as a compiler for PHP templates.

The Volt compiler allow you to extend it adding more functions, tests or filters to the existing ones.

Functions

Functions act as normal PHP functions, a valid string name is required as function name. Functions can be added using two strategies, returning a simple string or using an anonymous function. Always is required that the chosen strategy returns a valid PHP string expression:

<?php

use Phalcon\Mvc\View\Engine\Volt;

$volt = new Volt($view, $di);

$compiler = $volt->getCompiler();

// This binds the function name 'shuffle' in Volt to the PHP function 'str_shuffle'
$compiler->addFunction('shuffle', 'str_shuffle');

Register the function with an anonymous function. This case we use $resolvedArgs to pass the arguments exactly as were passed in the arguments:

<?php

$compiler->addFunction(
    'widget',
    function ($resolvedArgs, $exprArgs) {
        return 'MyLibrary\Widgets::get(' . $resolvedArgs . ')';
    }
);

Treat the arguments independently and unresolved:

<?php

$compiler->addFunction(
    'repeat',
    function ($resolvedArgs, $exprArgs) use ($compiler) {
        // Resolve the first argument
        $firstArgument = $compiler->expression($exprArgs[0]['expr']);

        // Checks if the second argument was passed
        if (isset($exprArgs[1])) {
            $secondArgument = $compiler->expression($exprArgs[1]['expr']);
        } else {
            // Use '10' as default
            $secondArgument = '10';
        }

        return 'str_repeat(' . $firstArgument . ', ' . $secondArgument . ')';
    }
);

Generate the code based on some function availability:

<?php

$compiler->addFunction(
    'contains_text',
    function ($resolvedArgs, $exprArgs) {
        if (function_exists('mb_stripos')) {
            return 'mb_stripos(' . $resolvedArgs . ')';
        } else {
            return 'stripos(' . $resolvedArgs . ')';
        }
    }
);

Built-in functions can be overridden adding a function with its name:

<?php

// Replace built-in function dump
$compiler->addFunction('dump', 'print_r');

Filters

A filter has the following form in a template: leftExpr name(optional-args). Adding new filters is similar as seen with the functions:
<?php

// This creates a filter 'hash' that uses the PHP function 'md5'
$compiler->addFilter('hash', 'md5');
<?php

$compiler->addFilter(
    'int',
    function ($resolvedArgs, $exprArgs) {
        return 'intval(' . $resolvedArgs . ')';
    }
);

Built-in filters can be overridden adding a function with its name:

<?php

// Replace built-in filter 'capitalize'
$compiler->addFilter('capitalize', 'lcfirst');

Extensions

With extensions the developer has more flexibility to extend the template engine, and override the compilation of a specific instruction, change the behavior of an expression or operator, add functions/filters, and more.

An extension is a class that implements the events triggered by Volt as a method of itself. For example, the class below allows to use any PHP function in Volt:

<?php

class PhpFunctionExtension
{
    /**
     * This method is called on any attempt to compile a function call
     */
    public function compileFunction($name, $arguments)
    {
        if (function_exists($name)) {
            return $name . '('. $arguments . ')';
        }
    }
}

The above class implements the method compileFunction which is invoked before any attempt to compile a function call in any template. The purpose of the extension is to verify if a function to be compiled is a PHP function allowing to call it from the template. Events in extensions must return valid PHP code, this will be used as result of the compilation instead of the one generated by Volt. If an event doesn’t return an string the compilation is done using the default behavior provided by the engine.

The following compilation events are available to be implemented in extensions:

Event/Method Descripción
compileFunction Triggered before trying to compile any function call in a template
compileFilter Triggered before trying to compile any filter call in a template
resolveExpression Triggered before trying to compile any expression. This allows the developer to override operators
compileStatement Triggered before trying to compile any expression. This allows the developer to override any statement

Volt extensions must be in registered in the compiler making them available in compile time:

<?php

// Register the extension in the compiler
$compiler->addExtension(
    new PhpFunctionExtension()
);

Caching view fragments

With Volt it’s easy cache view fragments. This caching improves performance preventing that the contents of a block from being executed by PHP each time the view is displayed:

```twig{% cache ‘sidebar’ %} {% endcache %}


Setting a specific number of seconds:

```twig{# cache the sidebar by 1 hour #}
{% cache 'sidebar' 3600 %}
    <!-- generate this content is slow so we are going to cache it -->
{% endcache %}

Any valid expression can be used as cache key:

```twig{% cache (‘article-‘ ~ post.id) 3600 %}

<h1>{{ post.title }}</h1>

<p>{{ post.content }}</p>

{% endcache %}


The caching is done by the `Phalcon\Cache` component via the view component. Learn more about how this integration works in the section [Caching View Fragments](views#caching-fragments).

## Inject Services into a Template

If a service container (DI) is available for Volt, you can use the services by only accessing the name of the service in the template:

```twig{# Inject the 'flash' service #}
<div id='messages'>{{ flash.output() }}</div>

{# Inject the 'security' service #}
<input type='hidden' name='token' value='{{ security.getToken() }}'>

Stand-alone component

Using Volt in a stand-alone mode can be demonstrated below:

<?php

use Phalcon\Mvc\View\Engine\Volt\Compiler as VoltCompiler;

// Create a compiler
$compiler = new VoltCompiler();

// Optionally add some options
$compiler->setOptions(
    [
        // ...
    ]
);

// Compile a template string returning PHP code
echo $compiler->compileString(
    "hello"
);

// Compile a template in a file specifying the destination file
$compiler->compileFile(
    'layouts/main.volt',
    'cache/layouts/main.volt.php'
);

// Compile a template in a file based on the options passed to the compiler
$compiler->compile(
    'layouts/main.volt'
);

// Require the compiled templated (optional)
require $compiler->getCompiledTemplatePath();

External Resources