Question

PHP:
run function when a specific class method is run

what I want is to run some additional functions when a class method is run without altering the already existing class.

how?

Answer 1

With a decorator:

class MyClassDecorator
{
    protected $decoratedInstance;

    public function __construct($decoratedInstance)
    {
        $this->decoratedInstance = $decoratedInstance;
    }

    public function methodNameInOriginalClass()
    {
        $this->decoratedInstance->methodIWantToRunBefore();
        $this->decoratedInstance->methodNameInOriginalClass();
        $this->decoratedInstance->methodIWantToRunAfter();
    }

    public function __call($method, $args)
    {
        if (method_exists($this->decoratedInstance, $method)) {
            return call_user_func_array(
                array($this->decoratedInstance, $method), 
                $args
            );
        }
    }
}

The above assumes that the methods you want to call are public on the $decoratedInstance.