Redefining PHP function?

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().

Answer 2

If you mean overloading in a Java sense, then the answer is no, this is not possible.

Quoting the PHP manual on functions:

PHP does not support function overloading, nor is it possible to undefine or redefine previously-declared functions.

You could use the runkit extension but usage of runkit in production scenarios is generally considered doubtful practice. If you want to exchange algorithms at runtime, have a look at the Strategy pattern or Anonymous functions instead.

If by redefine you mean add to an existing userland function, refactor, substitute or rewrite, then yes: it is as simple as you've shown. Just add the additional code to the function, but make sure you set a default for backwards compatibility.

Another option would be to use http://antecedent.github.io/patchwork

Patchwork is a PHP library that makes it possible to redefine user-defined functions and methods at runtime, loosely replicating the functionality runkit_function_redefine in pure PHP 5.3 code, which, among other things, enables you to replace static and private methods with test doubles.