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Date: Wed, 4 Mar 2009 03:01:55 -0800
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To: PHP Developers Mailing List <internals@lists.php.net>
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Subject: How expensive are function_exists() calls?
From: mike503@gmail.com (mike)

I am trying to figure out a strategy for multiple output formats on a
site, and it seems like I can have functions defined by default, but
have them defined -after- I've included the targetted format first.

However that would require

file1.php:

function foo() {}

file2.php

if(!function_exists('foo')) {
   function foo() {}
}

Is this a very expensive thing to do? There would be a good number of
functions that would be leveraging this. Is it a no-no? or is it
pretty cheap?

Thanks
- mike