Adding a custom function to an already instantiated object in PHP?

Question

What's the best way to do something like this in PHP?:

$a = new CustomClass();

$a->customFunction = function() {
    return 'Hello World';
}

echo $a->customFunction();

(The above code is not valid.)

Answer 1

Here is a simple and limited monkey-patch-like class for PHP. Methods added to the class instance must take the object reference ($this) as their first parameter, python-style. Also, constructs like parent and self won't work.

OTOH, it allows you to patch any callback type into the class.

class Monkey {

    private $_overload = "";
    private static $_static = "";


    public function addMethod($name, $callback) {
        $this->_overload[$name] = $callback;
    }

    public function __call($name, $arguments) {
        if(isset($this->_overload[$name])) {
            array_unshift($arguments, $this);
            return call_user_func_array($this->_overload[$name], $arguments);
            /* alternatively, if you prefer an argument array instead of an argument list (in the function)
            return call_user_func($this->_overload[$name], $this, $arguments);
            */
        } else {
            throw new Exception("No registered method called ".__CLASS__."::".$name);
        }
    }

    /* static method calling only works in PHP 5.3.0 and later */
    public static function addStaticMethod($name, $callback) {
        $this->_static[$name] = $callback;
    }

    public static function __callStatic($name, $arguments) {
        if(isset($this->_static[$name])) {
            return call_user_func($this->_static[$name], $arguments);
            /* alternatively, if you prefer an argument list instead of an argument array (in the function)
            return call_user_func_array($this->_static[$name], $arguments);
            */
        } else {
            throw new Exception("No registered method called ".__CLASS__."::".$name);
        }
    }

}

/* note, defined outside the class */
function patch($this, $arg1, $arg2) {
    echo "Arguments $arg1 and $arg2\n";
}

$m = new Monkey();
$m->addMethod("patch", "patch");
$m->patch("one", "two");

/* any callback type works. This will apply `get_class_methods` to the $m object. Quite useless, but fun. */
$m->addMethod("inspect", "get_class_methods");
echo implode("\n", $m->inspect())."\n";