Question

If I have a function:

function this($a){
   return $a;
}

If I wanted to redefine the function, would it be as simple as rewriting it?

function this($a, $b){  //New this function
   return $a * $b;
}

Answer 1

Nope, that throws an error:

Fatal error: Cannot redeclare foo()

The runkit provides options, including runkit_function_rename() and runkit_function_redefine().