How to write your own PHP templating engine
MVC is all the rage. Choosing a framework, however, is not so easy. The view part of a standard php MVC framework usually involves grabbing one or more model objects and printing out some text (html) about them. There are several frameworks that do this, including the famous smarty. There are even more frameworks, like Zend and CakePHP that include templating as a subset of what they do.
You may not have realized that PHP is itself a templating engine. It allows you to intersperse logic and text, and has some handy features to make it easy. I’m going to show you how to build a php-based templating framework in one file.
Please read Template Engines and Beyond Template Engine for background and other approaches to the same thing. They specifically address why you would want to use PHP instead of another layer for templating.
The final product
post.php?id=2
<?php
require_once('SimpleTemplate.php');
$post = new BlogPost($_GET["id"]); // pretend we're fetching a post from a db
$main = new SimpleTemplate("templating/post_full.php");
$main->post = $post;
$main->comments = $post->comments;
$layout = new SimpleTemplate("templating/main_layout.php");
$layout->title = "Post - $post->title";
$layout->content = $main->run();
echo $layout;templating/post_full.php
<h2><?= $post->title ?></h2>
<p><?= $post->body ?></p>
<hr>
<? foreach ($comments as $comment): ?>
<p>Comment - <?= "$comment->name - $comment-text" ?></p>
<? endforeach; ?>
<!-- Add a comment form here -->templating/main_layout.php
<html>
<head>
<!-- some script tags, css, etc -->
<title><?= $title ?></title>
</head>
<body>
<h1>This is my site</h1>
<?= $content ?>
</body>
</html>It’s simple to use, and requires nothing but basic php skills (maybe with the addition of knowing you can do that colon trick with loops).
How to make one?
It’s simple, really. First let’s create the class, and add 3 fields. source will store the variables, path is the path to the template, and result contains the generated result.
class SimpleTemplate
{
public $source;
public $path;
public $result;
}The main essential feature is that the engine include another php script and capture its output. You can easily do that with php’s output buffer functions. Let’s create a “run” function that will return the template’s content. Anything printed or echoed between ob_start() and ob_get_contents() will be stored in $this->result.
public function run()
{
ob_start();
extract ($this->source);
include $this->path;
$this->result = ob_get_contents();
ob_end_clean();
return $this->result;
}Next we need a way to store some variables so that extract call works. extract takes the variables available in a certain scope and empties them into the current scope. So, we can set $template->title = "a title"; and that variable will be available in our template as $title. We’ll implement php’s magic __set() and __get() to do this.
public function __set($name, $value)
{
$this->source[$name] = $value;
}
public function __get($name)
{
return isset($this->source[$name]) ? $this->source[$name] : "";
}Now that extract call will work as explained above. Finally, let’s add a __toString() method so we can just print $template; and use string concatenation and go nuts. Let’s also add a constructor that stores the $path variable.
<?php
class SimpleTemplate
{
public $source;
public $path;
public $result;
public function SimpleTemplate($path=false)
{
$this->source = array();
$this->path($path);
}
public function __toString()
{
return $this->run();
}
public function __set($name, $value)
{
$this->source[$name] = $value;
}
public function __get($name)
{
return isset($this->source[$name]) ? $this->source[$name] : "";
}
public function run()
{
ob_start();
extract ($this->source);
include $this->path;
$this->result = ob_get_contents();
ob_end_clean();
return $this->result;
}
}You can get more fancy if you like. In the full example I added parents for templates, meaning they can access variables from their parent’s scope. I also added the extract method, which copies all the variables in an object into the scope (it saves a few characters).
