Is it possible to overwrite a function in PHP

Can you declare a function like this...

function ihatefooexamples(){
  return "boo-foo!";
};

And then redeclare it somewhat like this...

if ($_GET['foolevel'] == 10){
  function ihatefooexamples(){
    return "really boo-foo";
  };
};

Is it possible to overwrite a function that way?

Any way?

Solution 1:

Edit

To address comments that this answer doesn't directly address the original question. If you got here from a Google Search, start here

There is a function available called override_function that actually fits the bill. However, given that this function is part of The Advanced PHP Debugger extension, it's hard to make an argument that override_function() is intended for production use. Therefore, I would say "No", it is not possible to overwrite a function with the intent that the original questioner had in mind.

Original Answer

This is where you should take advantage of OOP, specifically polymorphism.

interface Fooable
{
    public function ihatefooexamples();
}

class Foo implements Fooable
{
    public function ihatefooexamples()
    {
        return "boo-foo!";
    }
}

class FooBar implements Fooable
{
    public function ihatefooexamples()
    {
        return "really boo-foo";
    }
}

$foo = new Foo();

if (10 == $_GET['foolevel']) {
    $foo = new FooBar();
}

echo $foo->ihatefooexamples();

Solution 2:

Monkey patch in namespace php >= 5.3

A less evasive method than modifying the interpreter is the monkey patch.

Monkey patching is the art of replacing the actual implementation with a similar "patch" of your own.

Ninja skills

Before you can monkey patch like a PHP Ninja we first have to understand PHPs namespaces.

Since PHP 5.3 we got introduced to namespaces which you might at first glance denote to be equivalent to something like java packages perhaps, but it's not quite the same. Namespaces, in PHP, is a way to encapsulate scope by creating a hierarchy of focus, especially for functions and constants. As this topic, fallback to global functions, aims to explain.

If you don't provide a namespace when calling a function, PHP first looks in the current namespace then moves down the hierarchy until it finds the first function declared within that prefixed namespace and executes that. For our example if you are calling print_r(); from namespace My\Awesome\Namespace; What PHP does is to first look for a function called My\Awesome\Namespace\print_r(); then My\Awesome\print_r(); then My\print_r(); until it finds the PHP built in function in the global namespace \print_r();.

You will not be able to define a function print_r($object) {} in the global namespace because this will cause a name collision since a function with that name already exists.

Expect a fatal error to the likes of:

Fatal error: Cannot redeclare print_r()

But nothing stops you, however, from doing just that within the scope of a namespace.

Patching the monkey

Say you have a script using several print_r(); calls.

Example:

<?php
     print_r($some_object);
     // do some stuff
     print_r($another_object);
     // do some other stuff
     print_r($data_object);
     // do more stuff
     print_r($debug_object);

But you later change your mind and you want the output wrapped in <pre></pre> tags instead. Ever happened to you?

Before you go and change every call to print_r(); consider monkey patching instead.

Example:

<?php
    namespace MyNamespace {
        function print_r($object) 
        {
            echo "<pre>", \print_r($object, true), "</pre>"; 
        }

        print_r($some_object);
        // do some stuff
        print_r($another_object);
        // do some other stuff
        print_r($data_object);
        // do more stuff
        print_r($debug_object);
    }

Your script will now be using MyNamespace\print_r(); instead of the global \print_r();

Works great for mocking unit tests.

nJoy!

Solution 3:

Have a look at override_function to override the functions.

override_function — Overrides built-in functions

Example:

override_function('test', '$a,$b', 'echo "DOING TEST"; return $a * $b;');

Solution 4:

short answer is no, you can't overwrite a function once its in the PHP function scope.

your best of using anonymous functions like so

$ihatefooexamples = function()
{
  return "boo-foo!";
}

//...
unset($ihatefooexamples);
$ihatefooexamples = function()
{
   return "really boo-foo";
}

http://php.net/manual/en/functions.anonymous.php