Abstract properties

Hi, Don't want to start a big discussion, but is there a concrete reason, why abstract properties (or "a kind of abstract") are not supported? I've learned, that "an interface [the concept, not the implementations within a language] is the sum of all accessible (--> public) methods and properties", what as far as I understand means, that properties could (and should) be defineable in concrete interfaces too interface Queue { public function enqueue($value); public function dequeue(); public $top; } // or abstract class Queue { abstract public function enqueue($value); abstract public function dequeue(); abstract public $top; } Of course in the second example the "abstract" is kind of useless, but it's for illustration. I've seen some cases (for example the example above), where it would be useful to define properties in interfaces, but instead I was forced to (in my eyes) misuse [1] methods. Right now I cannot safely write somethig like /** * Must have a $top property */ interface Queue { public function enqueue($value); public function dequeue(); } function foo(Queue $q) { doSomethingWithTop($q->top); } Because I can never ensure, that $top exists. I always have to work with isset() here (or of course I use a getter, as mentioned earlier), what takes a little bit from the "usefulness" of interfaces ^^ The interface feels incomplete. Would like to hear some opinions, or maybe a summary of earlier discussions about this topic :) Regards, Sebastian [1] I've also learned, that methods define behaviour and properties define the state. "$top" in the example is part of the state, thus calling a method to fetch the state feels wrong/like a hack (thats btw my opinion about getters/setters too; just to create a bridge to other concepts ;)). -- github.com/KingCrunch