Hi On Mar 24, 4:54 pm, Luke <kickingje...@gmail.com> wrote: > It's late, but I have to ask something though that it still don't > understand. Why *doesn't* prototype just add a reference to the parent-class > in subclasses? Like > > klass.prototype.superclass = superclass > > ...in Class.Create. Is it because the *this*-reference would go out of > scope?
You mean so you could reference it in instances via `this.superclass`? Because of the grandchild problem. When you look at implementing a superclass/subclass hierarchy with JavaScript, it's easy to create one that will work one level deep (Parent->Child). Making it work GrandParent->Parent->Child and deeper is difficult. Remember that `this` always refers to the actual object, so if your Child code calls the parent's `foo` via `this.superclass.foo.call(this)` (recall the `.call(this)` is needed to preserve `this`), that's fine and it works great. But what happens when the Parent's code then does `this.superclass.foo.call(this)`? Right! Exactly the same thing, because it's using the same property (`superclass`) of the same object (`this`), and so it calls *itself*. Infinite loop time. Here are a couple of examples. I haven't used Prototype, but I've done what Prototype would effectively be doing if it worked as you were suggesting above: http://jsbin.com/esalu5 <-- Parent->Child, all fine and dandy http://jsbin.com/esalu5/2 <-- GrandParent->Parent->Child, loop city There is *no* way to use a property on `this` (inherited from the prototype or otherwise) to refer to the superclass, not that works more than one level deep. It can't, because if you start with `this`, all levels are working with the same data. That's why I based my mechanism on the actual function objects themselves; they're unique, and they're right there to hand. :-) HTH, -- T.J. Crowder Independent Software Engineer tj / crowder software / com www / crowder software / com -- You received this message because you are subscribed to the Google Groups "Prototype & script.aculo.us" group. To post to this group, send email to prototype-scriptaculous@googlegroups.com. To unsubscribe from this group, send email to prototype-scriptaculous+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/prototype-scriptaculous?hl=en.
