Smarty is a template engine for PHP. More specifically, it facilitates a manageable way to separate application logic and content from its presentation. This is best described in a situation where the application programmer and the template designer play different roles, or in most cases are not the same person.
For example, let's say you are creating a web page that is displaying a newspaper article.
The article $headline, $tagline,
$author and $body are
content elements, they contain no information about how they will be
presented. They are passed into Smarty
by the application.
Then the template designer edits the templates and uses a combination of HTML tags and template tags to format the presentation of these variables with elements such as tables, div's, background colors, font sizes, style sheets, svg etc.
One day the programmer needs to change the way the article content is retrieved, ie a change in application logic. This change does not affect the template designer, the content will still arrive in the template exactly the same.
Likewise, if the template designer wants to completely redesign the templates, this would require no change to the application logic.
Therefore, the programmer can make changes to the application logic without the need to restructure templates, and the template designer can make changes to templates without breaking application logic.
One design goal of Smarty is the separation of business logic and presentation logic.
This means templates can certainly contain logic under the condition that it is for presentation only. Things such as including other templates, alternating table row colors, upper-casing a variable, looping over an array of data and displaying it are examples of presentation logic.
This does not mean however that Smarty forces a separation of business and presentation logic. Smarty has no knowledge of which is which, so placing business logic in the template is your own doing.
Also, if you desire no logic in your templates you certainly can do so by boiling the content down to text and variables only.
Some of Smarty's features:
It is extremely fast.
It is efficient since the PHP parser does the dirty work.
No template parsing overhead, only compiles once.
It is smart about recompiling only the template files that have changed.
You can easily create your own custom functions and variable modifiers, so the template language is extremely extensible.
Configurable template
{delimiter} tag
syntax, so you can use
{$foo}, {{$foo}},
<!--{$foo}-->, etc.
The
{if}..{elseif}..{else}..{/if}
constructs are passed to the
PHP parser, so the {if...} expression syntax can be as
simple or as complex an evaluation as you like.
Allows unlimited nesting of
sections, if's etc.
Built-in caching support
Arbitrary template sources
Template Inheritance for easy management of template content.
Plugin architecture