Signals / Events in PHP

There are 3 projects I know of that could do with a more native way to implement Events

• debug callback on dbdo
• observer in PEAR_Exception (and eventually Warning)
• php-gtk

C# has a relatively new way of implementing this (while not perfect, it is interesting)

in abbreviated C# syntax this is what it looks like.

class xxxx {

      virtual method_prototype(x,y);
      public event eventvar method_prototype;

     public  somemethod() {
        eventvar += new Delegate(mycallback);
	eventvar(); // initiate the signals.
     }
     public mycallback(x,y) {
          printf("eventvar fired");
     }
}

In more natural PHP code, this cold be:

class xxxx {
      // event registers a method, that hooks into the generic event handler.
      public event $onDebug = array();

      
      function somemethod() {

        // add a handler to an event..
	// this is the natrual syntax for this, but does open the door to someone wiping the stack!
        $this->onDebug[] = array($this,'mycallback');


	// initiate the signals.
	$this->onDebug($x,$y);
     }
     // a handler..
     function mycallback($x,$y) {
	echo "debug hander got $x , $y\n";
     }
}

What would be involved in implementing this?

• event  recognize by tokenizer/parser (a string) ? do we have typehints for object args? -that would help..
  
• when parsing, register a method that  points to a generic signal emitor)
• the signal emitor just tests all the elements in the variable, and trys to call them...

Example implementation in PHP: (eg. what it would replaced if it was done at the engine level)

    
class myClass {
	/* This is the bit that is implemented by the sytnax "public static event $onDebug;" */
	static var $onDebug = array();
        static function onDebug() {
		foreach(myClass::$onDebug as &$call) {
			// handler returns true to block other events.
			if (call_user_func_args($call, func_get_args())) {
				return;
			}
		}
	}
	

	function doSomething() {
		self::onDebug("calling doSomething");
	}
}

function mydebugger($str) { 
	echo "DEBUG: $str\n";
}
// register an event handler 
myClass::$onDebug[] = 'mydebugger';


$x = new myClass();
$x->doSomething(); // prints DEBUG: calling doSomething