Trigger an event when a function is called in a class

Question

Is is possible in PHP to trigger an event whenever a function in a class is called, without adding it to every function in the class?

Example:

<?php
    class A {
        function xxx() {
            //this function will be called everytime I call another function in this class  
        }

        public static function b() {
            return 'Hello Stackoverflow!';
        }

        public static function c() {
            //I also want this function to trigger the event!
        }
    }

    echo A::b();
?>

Answer 1

AFAIK there are no native language constructs for this. If you need it for debugging purposes I would advice you to have deeper look into the xdebug extension especially function traces (awesome! :)

Another idea would be to implement __call() in your class and wrap all public methods. But this requires to change the code and has other side effects:

(simplified example)

class Test {

    protected $listeners;

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

    private function a() {
        echo 'something';
    }

    private function b() {
        echo 'something else';
    }

    public function __call($fname, $args) {
        call_user_func_array(array($this, $fname), $args);
        foreach($this->listeners as $listener) {
            $listener->notify('fname was called');
        }
    }

    public function addListener(Listener $listener) {
        $this->listeners[]= $listener;
    }
}

.

 class Listener {

     public function notify($message) {
         echo $message;
     }

 }

Example:

 $t = new Test();
 $l = new Listener();
 $t->addListener($l);

 $t->a();

Answer 2

This is a classic task for aspect oriented programming (AOP). PHP has no native support for AOP, however, there are some frameworks that make AOP in PHP possible. One of these is the GO! AOP PHP framework. You can also implement AOP using runkit.