Redefine Class Methods or Class

Is there any way to redefine a class or some of its methods without using typical inheritance? For example:

class third_party_library {
    function buggy_function() {
        return 'bad result';
    }
    function other_functions(){
        return 'blah';
    }
}

What can I do to replace buggy_function()? Obviously this is what I would like to do

class third_party_library redefines third_party_library{
    function buggy_function() {
        return 'good result';
    }
    function other_functions(){
        return 'blah';
    }
}

This is my exact dilemma: I updated a third party library that breaks my code. I don't want to modify the library directly, as future updates could break the code again. I'm looking for a seamless way to replace the class method.

I've found this library that says it can do it, but I'm wary as it's 4 years old.

EDIT:

I should have clarified that I cannot rename the class from third_party_library to magical_third_party_library or anything else because of framework limitations.

For my purposes, would it be possible to just add a function to the class? I think you can do this in C# with something called a "partial class."

Solution

It's called monkey patching. But, PHP doesn't have native support for it.

Though, as others have also pointed out, the runkit library is available for adding support to the language and is the successor to classkit. And, though it seemed to have been abandoned by its creator (having stated that it wasn't compatible with PHP 5.2 and later), the project does now appear to have a new home and maintainer.

I still can't say I'm a fan of its approach. Making modifications by evaluating strings of code has always seemed to me to be potentially hazardous and difficult to debug.

Still, runkit_method_redefine appears to be what you're looking for, and an example of its use can be found in /tests/runkit_method_redefine.phpt in the repository:

runkit_method_redefine('third_party_library', 'buggy_function', '',
    'return \'good result\''
);