Question

Snippet 1 works. Snippet 2 doesn’t. Why?

1.

foo();

function foo()
{
    // do soemething
}

2.

foo();

if(!function_exists("foo"))
{
    function foo()
    {
        // do soemething
    }
}

Answer 1

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

Functions need not be defined before
they are referenced, except when a
function is conditionally defined […]
Its definition must be processed prior
to being called.