All PHP functions have the global scope

http://php.net/manual/en/functions.user-defined.php

http://stackoverflow.com/a/14753616

 

The following codes use this feature for setting hex2bin() compartible in a class MyClass on PHP5.

 

class MyClass

{

public function __construct()

{

self::compat();

}

 

private static function compat()

{

if (!function_exists('hex2bin')) {

function hex2bin($hexString)

{

return pack('H*', $hexString);

}

}

}

 

public function foo($string)

{

return 'Hello '.hex2bin($string);

}

}

 

$MyObj = new MyClass();

echo $MyObj->foo('776f726c64');