Template Inheritance {#advanced.features.template.inheritance}

Inheritance brings the concept of Object Oriented Programming to templates, allowing you to define one (or more) base templates that can be extended by child templates. Extending means that the child template can override all or some of the parent named block areas.

The inheritance tree can be as deep as you want, meaning you can extend a file that extends another one that extends another one and so on.
The child templates can not define any content besides what\'s inside {block} tags they override. Anything outside of {block} tags will be removed.
The content of {block} tags from child and parent templates can be merged by the append or prepend {block} tag option flags and {$smarty.block.parent} or {$smarty.block.child} placeholders.
Template inheritance is a compile time process which creates a single compiled template file. Compared to corresponding solutions based on subtemplates included with the {include} tag it does have much better performance when rendering.
The child template extends its parent defined with the {extends} tag, which must be the first line in the child template. Instead of using the {extends} tags in the template files you can define the whole template inheritance tree in the PHP script when you are calling fetch() or display() with the extends: template resource type. The later provides even more flexibility.

Note

When $compile_check is enabled, all files in the inheritance tree are checked for modifications upon each invocation. You may want to disable $compile_check on production servers for this reason.

Note

If you have a subtemplate which is included with {include} and it contains {block} areas it works only if the {include} itself is called from within a surrounding {block}. In the final parent template you may need a dummy {block} for it.

layout.tpl (parent)

<html>
<head>
  <title>{block name=title}Default Page Title{/block}</title>
  {block name=head}{/block}
</head>
<body>
{block name=body}{/block}
</body>
</html>

myproject.tpl (child)

{extends file='layout.tpl'}
{block name=head}
  <link href="/css/mypage.css" rel="stylesheet" type="text/css"/>
  <script src="/js/mypage.js"></script>
{/block}

mypage.tpl (grandchild)

{extends file='myproject.tpl'}
{block name=title}My Page Title{/block}
{block name=head}
  <link href="/css/mypage.css" rel="stylesheet" type="text/css"/>
  <script src="/js/mypage.js"></script>
{/block}
{block name=body}My HTML Page Body goes here{/block}

To render the above use

 $smarty->display('mypage.tpl');

The resulting output is

<html>
<head>
  <title>My Page Title</title>
  <link href="/css/mypage.css" rel="stylesheet" type="text/css"/>
  <script src="/js/mypage.js"></script>
</head>
<body>
My HTML Page Body goes here
</body>
</html>

Instead of using {extends} tags in the template files you can define the inheritance tree in your PHP script by using the extends: resource type.

The code below will return same result as the example above.

<?php
$smarty->display('extends:layout.tpl|myproject.tpl|mypage.tpl'); 
?>