The document provides an overview of key changes and new features in upgrading to Smarty 3 from Smarty 2. Some of the main changes include: 1) Smarty 3 only works with PHP 5, 2) delimiters must now have whitespace to be treated as tags, 3) special variables now have local scope, and 4) new features like template objects, inheritance, and in-template function definitions have been added. The document also provides examples of how to address errors when upgrading and demonstrates how to use new Smarty 3 features.

1. Smarty 3 overview
http://www.smarty.net/v3_overview
how to overcome the present difficulties while upgrading to smarty3
reference url
1. {$array|mod} and {$array|@mod} behave identical
2. Smarty 3 is PHP 5 only. It will not work with PHP 4
3. The use of {php} tags is deprecated. It can be enabled with $smarty-
>allow_php_tag=true.
4. == Delimiters and whitespace ==
Delimiters surrounded by whitespace are no longer treated as Smarty tags.
Therefore, { foo } will not compile as a tag, you must use {foo}. This change
Makes Javascript/CSS easier to work with, eliminating the need for {literal}.
This can be disabled by setting $smarty->auto_literal = false;
5. == Unquoted Strings ==
Smarty 2 was a bit more forgiving (and ambiguous) when it comes to unquoted
strings
in parameters. Smarty3 is more restrictive. You can still pass strings
without quotes
so long as they contain no special characters. (anything outside of A-Za-z0-
9_)
For example filename strings must be quoted
<source lang="smarty">
{include file='path/foo.tpl'}
</source>
6.== Extending the Smarty class ==
If you are extending
the Smarty class, its constructor is not called implicitly if the your child
class defines
its own constructor. In order to run Smarty's constructor, a call to
parent::__construct()
within your child constructor is required.
<source lang="php">
class MySmarty extends Smarty {
function __construct() {
parent::__construct();
// your initialization code goes here
}
}
</source>

2. 7.== Scope of Special Smarty Variables ==
In Smarty 2 the special Smarty variables $smarty.section... and
$smarty.foreach...
had global scope. If you had loops with the same name in subtemplates you
could accidentally
overwrite values of parent template.
In Smarty 3 these special Smarty variable have only local scope in the
template which
is defining the loop. If you need their value in a subtemplate you have to
pass them
as parameter.
<source lang="smarty">
{include file='path/foo.tpl' index=$smarty.section.foo.index}
</source>
8. == SMARTY_RESOURCE_CHAR_SET ==
Smarty 3 sets the constant SMARTY_RESOURCE_CHAR_SET to utf-8 as default
template charset.
This is now used also on modifiers like escape as default charset. If your
templates use
other charsets make sure that you define the constant accordingly. Otherwise
you may not
get any output.
9. == trigger_error() ==
The API function trigger_error() has been removed because it did just map to
PHP trigger_error.
However it's still included in the Smarty2 API wrapper
10. == Smarty constants ==
The constants
SMARTY_PHP_PASSTHRU
SMARTY_PHP_QUOTE
SMARTY_PHP_REMOVE
SMARTY_PHP_ALLOW
have been replaced with class constants
Smarty::PHP_PASSTHRU
Smarty::PHP_QUOTE
Smarty::PHP_REMOVE
Smarty::PHP_ALLOW
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11. == newline at {if} tags ==
A n was added to the compiled code of the {if},{else},{elseif},{/if} tags to
get output of newlines as expected by the template source.

3. If one of the {if} tags is at the line end you will now get a newline in the
HTML output.
12. == Autoloader ==
Smarty 3 does register its own autoloader with spl_autoload_register. If your
code has
an existing __autoload function then this function must be explicitly
registered on
the __autoload stack. See http://us3.php.net/manual/en/function.spl-autoload-
register.php
for further details.
13.== Plugin Filenames ==
Smarty 3 optionally supports the PHP spl_autoloader. The autoloader requires
filenames
to be lower case. Because of this, Smarty plugin file names must also be
lowercase.
In Smarty 2, mixed case file names did work.
new feature examples
http://www.smarty.net/v3_overview
1. Rewritten for PHP 5
2. New Lexer/Parser:
Smarty has a new template parser, a real syntax lexer. This gives Smarty much finer control over its
template syntax. Things like in-template math, line-precision error messages and recursive template
functions are now possible.
3. Template Objects
http://www.smarty.net/docs/en/api.create.template.tpl
You can now make template objects and execute them independently. Example:
$tpl = $smarty->createTemplate('my.tpl');
$tpl->assign('foo','bar');
$smarty->display($tpl); // or $tpl->display();
Data Objects:-
The variables assigned to a template can now be managed independently as a Smarty_Data object.
Example:

4. $data = new Smarty_Data;
$data->assign('foo','bar');
$smarty->display('my.tpl',$data);
$tpl = $smarty->createTemplate('my.tpl',$data);
Template Inheritance
Templates can now inherit from each other. You mark blocks of a template with {block
name=foo}{/block} tags, a template can inherit with the {extend file="my.tpl"} tag, and then you can
replace, change or append the blocked contents from the inheriting template(s).
Example:
parent .tpl
<html>
<head>
<title>{block name=title}default title{/block}<title>
</head>
<body>
{block name=body}default body{/block}
</body>
</html>
child .tpl
{extends file="parent.tpl"}
{block name=title}My Child Title{/block}
{block name=body}My Child Body{/block}
output of $smarty->display('child.tpl');
<html>
<head>
<title>My Child Title<title>
</head>
<body>
My Child Body
</body>
</html>

5. In-Template Function Definitions:-
Smarty
{* define the function *}
{function name=menu level=0}
<ul class="level{$level}">
{foreach $data as $entry}
{if is_array($entry)}
<li>{$entry@key}</li>
{menu data=$entry level=$level+1}
{else}
<li>{$entry}</li>
{/if}
{/foreach}
</ul>
{/function}
{* create an array to demonstrate *}
{$menu = ['item1','item2','item3' => ['item3-1','item3-2','item3-3' =>
['item3-3-1','item3-3-2']],'item4']}
{* run the array through the function *}
{menu data=$menu}
Output
* item1
* item2
* item3
o item3-1
o item3-2
o item3-3
+ item3-3-1
+ item3-3-2
* item4