Twig tips & tricks for advanced features, defensive templates and best practices

TWIG
tips & tricks
SUNSHINEPHP JAVIER EGUILUZ
FEBRUARY 8TH 2013

Thanks to sponsors and organizers

Adam Pablo
Culp Godel

About me

Javier Eguiluz
I’m a programmer
and trainer from Spain.

I’m a long-term Symfony enthusiast

My Symfony2 book

Agile web development
with Symfony2

My Symfony website

WINNER 2011
Best Symfony Blog

I’m the « A week of Symfony» guy

I’m the « A week of Symfony» guy

this is me!

Twig is...
• The best template engine for PHP.
• Fast, secure and modern.
• Easy to learn, to read and to write.
• If you don’t know Twig yet, read the
official docs at:
http://twig.sensiolabs.org/documentation

Agenda
• Tips and tricks about Twig.
• Advanced features.
• Defensive template design.
• Best practices.
• New and noteworthy Twig features.

Twig development activity is crazy!
(last 12 months) Twig Jinja2
(PHP, Symfony) (Python, Django)

Commits 525 11

Authors 35 5

Versions released 23 0

New and noteworthy

1 2 3 4 5

«template_from_string» function
{% set user_template = "{{ description[0:80] }}
<br/> Price: {{ product.price }}" %}

{% include
template_from_string(user_template) %}

«include» function
{% include 'template.twig' %}
{{ include('template.twig') }}
equivalent

«include» function WRONG
{% set content = include('index.twig') %}

OK
{% set content %}
{{ include('index.twig') }}
{% endset %}

«include» function WRONG
{{ include('index.twig')|striptags('<a>')[0:80] }}

{% set content %} OK
{{ include('index.twig') }}
{% endset %}

{{ content|striptags('<a>')[0:80] }}

«first» and «last» filters
{% set firstElement = array|first %}
{% set lastElement = array|last %}

{% set first = array[0] %}
{% set last = array[array|length - 1] %}

{% set first = array[0] %}
{% set last = array[array|length - 1] %}

only works for zero-
indexed numeric arrays

{{ [1, 2, 3, 4]|first }} 1

{{ { a: 1, b: 2, c: 3, d: 4 }|first }} 1

{{ '1234'|first }} 1

result

Named arguments
{{ text|convert_encoding('UTF-8', 'ISO-8859-1') }}

{{ text|convert_encoding(
to='UTF-8', from='ISO-8859-1') }}

from='ISO-8859-1', to='UTF-8') }}

Named arguments

to='UTF-8', from='ISO-8859-1') }}
equivalent

from='ISO-8859-1', to='UTF-8') }}

Named arguments

to='UTF-8', from='ISO-8859-1') }}
equivalent

from='ISO-8859-1', to='UTF-8') }}

argument order changed!

Named arguments
{{ "now"|date("Y-m-d", "America/New_York") }}
mandatory to set the
second argument

{{ "now"|date(timezone="America/New_York") }}
just set the argument
you need

Functions and filters before 1.12
$twig->addFunction('functionName',
new Twig_Function_Function('someFunction')
);

$twig->addFunction('otherFunction',
new Twig_Function_Method($this, 'someMethod')
);

Functions and filters in Twig 1.12
$twig->addFunction(new Twig_SimpleFunction(
'twig_function', 'some_php_function'
));
'twig_function', array($object, 'method_name')
));
'twig_function', function() { ... }
));

Functions and filters in Twig 1.12
'twig_function', 'some_php_function'
));
'twig_function', array($object, 'method_name')
));
'twig_function', function() { ... }
)); super cool

{% for i in array|sort %}
{# ... #}
{% endfor %}

How is the
array sorted?

{# ... #}
{% endfor %}

PHP defines 15 sorting functions
• asort() • array_multisort()
• arsort() • natcasesort()
• krsort() • natsort()
• ksort() • rsort()
• rsort() • shuffle()
• shuffle() • uasort()
• sort() • uksort()
• usort()

Overriding filters
• Where can I find the PHP function
used by Twig?
• How can I override it with my own
implementation?

Where Twig defines everything
lib/twig/Extension/Core.php
class Twig_Extension_Core extends Twig_Extension {
public function getTokenParsers() {
return array(

+1,300 lines
new Twig_TokenParser_For(),
new Twig_TokenParser_If(),

class!
new Twig_TokenParser_Extends(),
new Twig_TokenParser_Include(),
new Twig_TokenParser_Block(),
// ...
);
}

public function getFilters() {
$filters = array(
'format' => new Twig_Filter_Function('sprintf'),
'replace' => new Twig_Filter_Function('strtr'),
'abs' => new Twig_Filter_Function('abs'),
// ...
);

Where Twig defines everything
lib/twig/Extension/Core.php
class Twig_Extension_Core extends Twig_Extension {
public function getTokenParsers() {
return array( • Filters
new Twig_TokenParser_For(),
new Twig_TokenParser_If(),
new Twig_TokenParser_Extends(), • Functions
new Twig_TokenParser_Include(),
new Twig_TokenParser_Block(),
// ...
• Tags
• Operators
);
}

$filters = array( • Tests
'format' => new Twig_Filter_Function('sprintf'),
'replace' => new Twig_Filter_Function('strtr'),
'abs' => new Twig_Filter_Function('abs'),
// ...
);

«sort» filter uses «asort» function
new Twig_SimpleFilter('sort', 'twig_sort_filter'),

// ...

function twig_sort_filter($array)
{
asort($array);

return $array;
}

Overriding filters
✔ Where can I find the PHP function
•
used by Twig?
• How can I override it with my own
implementation?

Replace «asort» with «natcasesort»
// asort
A1, a0, a10, a2

// natcasesort
a0, A1, a2, a10

1. Define a new Twig extension
class MyCoreExtension
extends Twig_Extension_Core {
// ...
}

2. Define the new «sort» filter
class MyCoreExtension extends Twig_Extension_Core {
// ...
}
}

class MyCoreExtension extends Twig_Extension_Core {
return array_merge(
parent::getFilters(),
array( ... )
);
}
}

class MyCoreExtension extends Twig_Extension_Core
{
public function getFilters()
{
return array_merge(parent::getFilters(), array(
'sort' => new Twig_Filter_Method($this, 'sortFilter')
));
}

public function sortFilter($array)
{
natcasesort($array);
return $array;
}
}

3. Register the new extension
$twig = new Twig_Environment( ... );

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

This is now
natcasesort

{# ... #}
{% endfor %}

WordPress template tags
the_ID()
the_title()
the_time()
the_content()
the_category()
the_shortlink()

the_ID() class Post {
$id = ...
the_title() $title = ...
the_time() $time = ...
the_content() $content = ...
$category = ...
the_category() $shortlink = ...
the_shortlink() // ...
}

Variable functions
$twig->addFunction(
'the_*',
new Twig_Function_Function('wordpress')
);

function wordpress($property, $options)
{
// ...
}

Variable functions
$twig->addFunction(
'the_*',
new Twig_Function_Function('wordpress')
); don’t use regexps,
just asterisks
function wordpress($property, $options)
{
// ...
}

Variable functions in practice
{{ the_ID() }}
function wordpress('ID') { ... }

{{ the_content() }}
function wordpress('content') { ... }

Variable functions in practice
{{ the_title('<h3>', '</h3>') }}

function wordpress(
'title',
array('<h3>', '</h3>')
) { ... }

next_image_link()
next_post_link()
next_posts_link()
previous_image_link()
previous_post_link()
previous_posts_link()

next_image_link() next_*_link()
next_post_link() next_*_link()
next_posts_link() next_*_link()
previous_image_link() previous_*_link()
previous_post_link() previous_*_link()
previous_posts_link() previous_*_link()

next_image_link() *_*_link()
next_post_link() *_*_link()
next_posts_link() *_*_link()
previous_image_link() *_*_link()
previous_post_link() *_*_link()
previous_posts_link() *_*_link()

php_* dynamic function
$twig->addFunction(new Twig_SimpleFunction('php_*',
function() {
$arg_list = func_get_args();
$function = array_shift($arg_list);

return call_user_func_array($function, $arg_list);
},
array('pre_escape' => 'html', 'is_safe' => array('html')
));

Exposing PHP functions
{{ php_print_r(['value1', 'value2']) }}
{{ php_crypt('mypassword') }}
{{ php_memory_get_usage() }}
{{ php_uniqid() }}

Reference
http://github.com/lidaa/LidaaTwigBundle

{% source ‘...’ %}
file_get_contents()

The new «source» tag
{% source 'home.twig' %}
{% source '../../../composer.json' %}

How does Twig work internally
{% source
'simple.twig' %}
Twig PHP class
__TwigTemplate_06dff1ec7c2c
ceb3f45ac76fc059b730

template file
extends Twig_Template
{
public function
{# ... #} __construct(Twig_Environment
$env)
{
parent::__construct($env);

$this->parent = $this-
>env-
>loadTemplate("layout.twig");

$this->blocks = array(

Lexer Parser Compiler

How does Twig work internally
{% source
'simple.twig' %}
Twig PHP class
__TwigTemplate_06dff1ec7c2c
ceb3f45ac76fc059b730

template file
{
public function
{# ... #} __construct(Twig_Environment

you must
$env)
{
parent::__construct($env);

provide these
$this->parent = $this-
>env-
>loadTemplate("layout.twig");

$this->blocks = array(

Lexer Parser Compiler

1. Create a new token parser
class SourceTokenParser extends Twig_TokenParser
{
public function getTag()
{
return 'source';
}
}

2. Register the new token parser
$loader = new Twig_Loader_Filesystem(...);
$twig = new Twig_Environment($loader, array(...));

$twig->addTokenParser(
new SourceTokenParser()
);

3. Fill in the «parse» method
{
public function parse(Twig_Token $token)
{
$lineno = $token->getLine();
$value = $this->parser->getExpressionParser()
->parseExpression();

$this->parser->getStream()
->expect(Twig_Token::BLOCK_END_TYPE);

return new SourceNode($value, $lineno, $this->getTag());
}
}

3. Fill in the «parse» method
{
public function parse(Twig_Token $token)
{ this is hard
$lineno = $token->getLine();
$value = $this->parser->getExpressionParser()
->parseExpression();

$this->parser->getStream()
->expect(Twig_Token::BLOCK_END_TYPE);

return new SourceNode($value, $lineno, $this->getTag());
}
}

4. Define the node class that compiles tags
class SourceNode extends Twig_Node {
public function __construct(Twig_Node_Expression $value, $lineno, $tag = null) {
parent::__construct(array('file' => $value), array(), $lineno, $tag);
}

public function compile(Twig_Compiler $compiler) {
$compiler
-> // ...
->write('echo file_get_contents(')
->subcompile($this->getNode('file'))
->raw(');')
;
}
}

4. Define the node class that compiles tags
class SourceNode extends Twig_Node {
public function __construct(Twig_Node_Expression $value, $lineno, $tag = null) {
parent::__construct(array('file' => $value), array(), $lineno, $tag);
}

public function compile(Twig_Compiler $compiler) {
$compiler
-> // ... this is
->write('echo file_get_contents(') very hard
->subcompile($this->getNode('file'))
->raw(');')
;
}
}

The compiled PHP template
// line 3
echo file_get_contents("simple.twig");
// ...
{% source 'simple.twig' %}
// line 5
echo file_get_contents("../../../composer.json");

Most apps use a single loader
$loader = new Twig_Loader_Filesystem(
__DIR__.'/templates'
);
$twig = new Twig_Environment($loader, array());

$html = $twig->render('home.html.twig');

Chaining several loaders
$loader1 = new Twig_Loader_Filesystem(...);
$loader = new Twig_Loader_Chain(array(
$loader1, $loader2
));


// ...

Chaining different loaders
$loader2 = new Twig_Loader_Array(...);
$loader3 = new Twig_Loader_String(...);

$loader1, $loader2, $loader3
));

// ...

Chaining different loaders
$loader2 = new Twig_Loader_Array(...);
$loader3 = new Twig_Loader_String(...);

$loader1, $loader2, $loader3
));
order matters!
// ...

Adding loaders at runtime
$loader = new Twig_Loader_Filesystem('/templates');

if ( ... ) {
$twig->addLoader(
new Twig_Loader_Filesystem('/special_templates')
);
}

// ...

Storing templates in several folders
$loader = new Twig_Loader_Filesystem(array(
__DIR__.'/default',
__DIR__.'/templates',
__DIR__.'/themes'
));

// ...

Storing templates in several folders
$loader = new Twig_Loader_Filesystem(array(
__DIR__.'/default',
__DIR__.'/templates',
__DIR__.'/themes'
));
$twig = new Twig_Environment($loader,went wrong.
Whoops, looks like something array());

// ... Twig_Error_Loader: The "_DIR_/templates"
directory does not exist.

Adding folders at runtime

$path = $user_slug.'/templates';
if (file_exists($path)) {
$loader->addPath($path);
}


// ...

Prioritizing template folders

if(...) {
$loader->addPath($user_slug.'/templates');
$loader->prependPath($user_slug.'/themes');
}


// ...

Prioritizing template folders

if(...) {
$loader->addPath($user_slug.'/templates');
$loader->prependPath($user_slug.'/themes');
} path is added before
any other path

// ...

It’s difficult to prioritize folders
$loader
->addPath(...)
->addPath(...)
->prependPath(...)
->addPath(...)
->prependPath(...)
;

Namespaces are better than folders

templates/
themes/index.twig
admin/index.twig
frontend/index.twig

Namespaces are better than folders
$loader = new Twig_Loader_Filesystem(__DIR__.'/templates');

$html = $twig->render('admin/index.twig');
$html = $twig->render('themes/index.twig');
$html = $twig->render('frontend/index.twig');

App doesn’t work if folders change

templates/
themes/index.twig
frontend/index.twig

admin/

App doesn’t work if folders change

templates/
themes/index.twig
Whoops, looks like something went wrong.
frontend/index.twig
Twig_Error_Loader: The "admin/index.twig"

admin/
template does not exist.

Registering and using namespaces
$loader->addPath(__DIR__.'/admin', 'admin');

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

Registering and using namespaces
$loader->addPath(__DIR__.'/admin', 'admin');

$html = $twig->render('@admin/index.twig');
logical path
physical path

A practical use case
$loader->addPath(
__DIR__.'/themes/default/admin', 'backend'
);

// with namespaces
$html = $twig->render('@backend/edit.twig');

// with physical paths
$html = $twig->render('themes/default/admin/
edit.twig');

Twig.js = Twig inside JavaScript

TWIG
TWIG

TWIG
TWIG
HTML HTML

TWIG
TWIG
HTML HTML
JS

JS

TWIG
TWIG
HTML HTML
JS

JS TWIG

TWIG

«A tale of two twig.js»
twig.js by
Johannes Schmitt
http://github.com/schmittjoh/twig.js

twig.js by
John Roepke
https://github.com/justjohn/twig.js

twig.js by Johannes Schmitt
• A templating engine for Javascript
using Jinja/Twig style syntax.
• It compiles your Twig templates to
raw Javascript (to use the same
templates for both server and client).

Defining the template
{# tweet.twig #}
{% twig_js name="tweet" %}
<p>
{{ message }} <span>by {{ author }}</span>
<time datetime="{{ published_at|date }}">
{{ published_at|date }}
</time>
</p>

important!
{# tweet.twig #}
<p>
</time>
</p>

Rendering the template in the browser
<script type="text/javascript" src="twig.js"></script>
<script type="text/javascript" src="tweet.js"></script>
<script language="javascript" type="text/javascript">
var html = Twig.render(tweet, {
message: "...", author: "...", published_at: "..."
}));
</script>

«A tale of two twig.js»
twig.js by
Johannes Schmitt
http://github.com/schmittjoh/twig.js

twig.js by
John Roepke
http://github.com/justjohn/twig.js

twig.js by John Roepke
• A pure JavaScript implementation of
the Twig PHP templating language.
• The goal is to provide a library that is
compatible with both browsers and
server side node.js.

{# tweet.twig #} not necessary
<p>
</time>
</p>

var template = twig({data:
'<p> {{ message }} ... </p>' template’s
}); source code
var html = template.render({
});
</script>

Rendering the template in node.js
<script type="text/javascript">
var Twig = require("twig"), express = require('express'), app = express();

app.set("twig options", { strict_variables: false });

app.get('/tweet', function(req, res){
res.render('tweet.twig', {
});
});

app.listen(80);
</script>

A simple object
$offer = new Offer();
$offer->title = "Lorem Ipsum Dolor Sit Amet";
$offer->description = "Ut enim ad minim veniam ...";
$offer->commission = 20;

A simple object
$offer = new Offer();
$offer->title = "Lorem Ipsum Dolor Sit Amet";
$offer->description = "Ut enim ad minim veniam ...";
$offer->commission = 20;

TOP-SECRET
information

Templates can show any property
Offer data
----------
Title: {{ offer.title }}
Description: {{ offer.description }}
Commission: {{ offer.commission }}

Twitter Sandbox
• It’s a regular Twig extension.
• Disabled by default.
• It allows to restrict the functions,
filters, tags and object properties
used in the templates.
• It’s based on security policies.

Define a new security policy
$loader = new Twig_Loader_Filesystem('...');

$properties = array(
'Offer' => array('title', 'description')
);

$policy = new Twig_Sandbox_SecurityPolicy(
array(), array(), array(), $properties, array()
);


commission is

$properties = array( not included
'Offer' => array('title', 'description')
);

);

$properties = array('Offer' => array('title', 'description'));
);

$sandbox = new Twig_Extension_Sandbox(
$policy, true
);
$twig->addExtension($sandbox);

$properties = array('Offer' => array('title', 'description'));
);

$sandbox = new Twig_Extension_Sandbox(
$policy, true
); ALL templates are sandboxed
$twig->addExtension($sandbox);

The template now displays an error
Offer data
----------

The template now displays an error
Offer data
----------
Whoops, looks like something went wrong.
Calling "comission" property on a "Offer"
object is not allowed in ... at line 6.

Security policy arguments
$tags,
$filters,
$methods,
$properties,
$functions
);

Allow to use just 3 filters
$tags,
array('escape', 'upper', 'lower'),
$methods,
$properties,
$functions
);

Allow to use just 2 tags
array('include', 'extends'),
$filters,
$methods,
$properties,
$functions
);

Use any tag except include and extends
array_diff(
array_keys($twig->getTags()),
array('include', 'extends')
),
$filters,
$methods,
$properties,
$functions
);

Adding a trace to all web pages
<html>
<head> ... </head>

<body>
...

<span data-host="Darwin 10.8.0 ..."
data-elapsed="0.97804594039 sec."
data-timestamp="1339609672.9781">
</span>
</body>
</html>

cache/09/fc/2d8a188dda8245d295e6324582f2.php

/* homepage.html.twig */
class __TwigTemplate_09f8a...582f2
{
public function __construct(Twig_Environment $env) { ... }
protected function doGetParent(array $context) { ... }
protected function doDisplay(array $context, array $blocks) { ... }

// ...
}

The base template class
class __TwigTemplate_09f...2f2
{
// ...
}

lib/Twig/Template.php
abstract class Twig_Template {
public function render(array $context)
{
// ...
}
// ...

}

lib/Twig/Template.php
abstract class Twig_Template {
{
tweak this method
// ... to tweak templates
}
// ...

}

Use a different base template
$twig = new Twig_Environment($loader, array(
'base_template_class' => 'ACMEMyTwigTemplate',
));

# if you use Symfony2
# app/config/config.yml
twig:
base_template_class: "ACMEMyTwigTemplate"

The new base template class
class MyTwigTemplate extends Twig_Template
{
{
$trace = ...

return str_replace(
"</body>",
$trace."n</body>",
parent::render($context)
);
}
}

The new base template class
abstract class MyTwigTemplate extends Twig_Template
{
{
$trace = sprintf('<span data-host="%s" data-elapsed="%s sec."
data-timestamp="%s"></span>',
php_uname(),
microtime(true) - $_SERVER['REQUEST_TIME'],
microtime(true)
);
return str_replace("</body>", $trace."n</body>", parent::render($context));
}

Errors will happen

ERROR 500

ERROR

Errors will happen

ERROR 500

ERROR

users prefer this

Default values
{{ variable|default("value") }}

(discount {{ discount|default(0) }}%)
Hi {{ user_name|default("") }}!

The use_strict_variables option
'use_strict_variables’ => false
));

The use_strict_variables option
'use_strict_variables’ => false
));
inexistent variables won’t
produce a Twig error page

Ignore missing templates
{% include 'section_' ~ slug ~ '.twig'
ignore missing %}

Define fallback templates
{% extends [
'layout_' ~ locale ~ '.html.twig',
'layout.html.twig'
] %}

Use fallbacks and ignore errors
{% include [
'layout_' ~ locale ~ '.html.twig',
'layout.html.twig'
] ignore missing %}

Twig linter
• A linter detects syntax errors
automatically.
• Use it as a preventive measure to
detect errors before serving pages to
users.

Twig linter in practice
$twig = new Twig_Environment($loader, array(..));

try {
$twig->parse($twig->tokenize($plantilla));
echo "[OK]";
} catch (Twig_Error_Syntax $e) {
echo "[ERROR] There are some syntax errors";
}

INTEGRATING
TWITTER
BOOTSTRAP

Twitter Bootstrap grid model

3

Each row adds up to 12 columns

3

12 = 3 + 9


3

12 = 3 + 4 + 5


3

12 = 3 + 2 + 3 + 4

Most grids are based on 2 or 3 columns

3

2 columns

Most grids are based on 2 or 3 columns

3

3 columns

reuse a fixed
structure

extends + include = embed

reuse a fixed reuse
structure contents


reuse a fixed reuse
structure contents

reuse contents and a
flexible structure

Reusable 2-column grid
{# grid_2.twig #}
<div class="row">
<div class="{{ col1_span }} {{ col1_offset }}">
{% block column1 %}{% endblock %}
</div>

<div class="{{ col2_span }} {{ col2_offset }}">
{% block column2 %}{% endblock %}
</div>
</div>

2-column grid in practice
{% embed 'grid_2.twig' with { 'col1_span': 'span9',
'col2_span': 'span3' } %}

{% block column1 %} {# ... #} {% endblock %}


{% endembed %}

{% embed 'grid_2.twig' with { 'col1_span':Magic
Twig 'span9',
in progress...
'col2_span': 'span3' } %}



{% endembed %}

{% embed 'grid_2.twig' with { 'layout': '9_3' } %}



{% endembed %}

{% embed 'grid_2.twig' with { 'layout': '9_3' } %}

{% set col1_span = layout|split('_')[0:]|join %}

3-column grid
{% embed 'grid_3.twig' with { 'layout': '3_6_3' } %}




{% endembed %}

3-column grid
{% embed 'grid_3.twig' with { 'layout': '3_6_3' } %}


Recap
• New and noteworthy • Sandbox
• Overriding filters • Base template
• Dynamic functions • Defensive design
• Custom tags • Embed tag
• Template loaders
• Namespaces
• Twig.js

Contact me
• javier.eguiluz@gmail.com
• linkedin.com/in/javiereguiluz
• twitter.com/javiereguiluz
• github.com/javiereguiluz

Twig tips & tricks for advanced features, defensive templates and best practices

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Twig tips & tricks for advanced features, defensive templates and best practices