php many elseif statements better performance

How about this?

$templates = array('search',
                   'newsletter',
                   'product',
                   'categories',
                   'about',
                   'sitemap',
                   'index');

foreach ($templates as $template)
{
    if (isset($_GET[$template]))
    {
        include_once "template/template.$template.php";
        break;
    }
}

You really should specify an array of valid templates—it's much safer.

I guess an alternative is to search the other way around:

$templates = array('search',
                   'newsletter',
                   'product',
                   'categories',
                   'about',
                   'sitemap',
                   'index');

foreach ($_GET as $key => $val)
{
    if (in_array($key, $templates))
    {
        include_once "template/template.$key.php";
        break;
    }
}

Assuming $_GET holds only the includes you can do:

foreach ($_GET as $key => $val){
    if(isset($key)){
        include_once 'template/template.'.$val.'.php';
        break;
    }
}

Just a few passing thoughts...

• performance here is not an issue at all.
  Even a serie of ifs withouth elses would be executed in a few microseconds.

Code maintenability and robustness is an issue, though.

I find the slightly hackish use of switch somewhat unsatisfactory or even dangerous, because

• the important information (the GET index and the actual page name) is still duplicated and burried in a glob of repetitive code,
• the switch will behave oddly if two conditions happen to be true simultaneously (I suppose it will take the first satisfied condition, but still that's not very clean)
• adding or removing a page still requires to duplicate/erase 3 or 4 lines of code, and inadvertently duplicating a block might go unnoticed and put the programmer in the annoying "I'm sure this matter was settled (but it actually wasn't)" situation.

As a matter of fact, I find the interface a bit strange. Passing a single "target" variable that would enumerate the possible pages seems more consistent to me. That would eliminate the odd cases where two page selection flags would be set simultaneously.

You can then have a simple list of targets and either compute the name of the target pages or have them stored in an assoc array (if you really can't name them in a consistent way, although I wonder what strange requirement would prevent you from doing that).

The key points I would consider for robustness are

• no data duplication
• no "lazy" default case (unless the default value comes from a functional requirement)

For all these reasons, I would change the way the page is selected, like so:

$pages = array (                  // single data source
    "search",
    "newsletter",
    // etc...
    );
@$page = $pages=[$_GET["page"]];  // single page selector
if (!$page) $page = "index";      // explicit default case

include "template/template.$page.php"; // no reason to include only once

// if someone else happens to include the template, better have the page
// break down immediately and correct the problem than letting a piece of
// buggy code live happily somewhere in your scripts

You can use an array: if you find the key inside, use it, otherwise just use default :

<?php
$tpl = array(
'search' => 'template/template.search.php',
'newsletter' => 'template/template.newsletter.php',
'product' => 'template/template.product.php'
#...
);

foreach($_GET as $get){
   if(array_key_exists($get, $tpl)) include_once($tpl[$get]); // assuming search is within $get
}

?>

You could use a variable (like t) in the query string to indicate the template you want to use, and then just include the template name dynamically based on that. So if your URL looks something like: mysite.com/page.php?t=newsletter&blah=1&..., then all you need to do is:

include_once('template/template.' . $_GET['t'] . '.php');