Comments on: Constructor Function

By: jackson

jackson — Sun, 01 Nov 2009 01:49:12 +0000

A Google search for "as3 reflection" or "as3 reflect" doesn't take you to that project. I found their Google Code page though and dug around to find the source. It is indeed similar to my implementation. Anyone interested in a more complete library of reflection functions should check it out. I assure you though, I reached this solution without any knowledge of the "AS3 Commons" Google Code project. Thanks for pointing it out though; it's always nice to peruse open source AS3 to see what others are up to.

By: gio

gio — Sun, 01 Nov 2009 01:02:58 +0000

If someone ever needs a way to dynamically…
- find the type of a class from an istance (that could happen to be of one in many different types…)
- create a new instance of the same class (whatever the constructor signature this class type has…)

a search on as3 reflection should take them to “as3 reflect” project on google code, where the
org.as3commons.lang.ClassUtils.newInstance()
method does exactly what ‘your’ MakeConstructorFunction does…

By: jackson

jackson — Fri, 23 Oct 2009 20:49:24 +0000

Having a Function object for a constructor means that you have the same type of object as with all the other methods of a class. Having a Class means that you have a problem in that you have a different type and therefore any variable that will hold a function of a class must be untyped (Object or *) and then that you must write logic to check which type you have before “calling” it:

if (func is Function)
{
    result = func();
}
else if (func is Class)
{
    result = new func();
}
else
{
    // now I have an error to handle
}

This could be useful for a variety of purposes, but most of them are examples of the above observation. One such example is that you might have a function that takes a Function, not a Class or an Object, such as addEventListener(), which you cannot or do not want to change. I can’t give you the real world example that I needed this for, but suffice it to say that dealing with both Class and Function types would have been extremely annoying.

It may be that you never have usage for makeConstructorFunction. In fact, I think most people probably won’t. But if you ever do, I hope you remember where you read about it. :)

By: Ben Clinkinbeard

Ben Clinkinbeard — Fri, 23 Oct 2009 20:33:23 +0000

I guess what I don’t understand is If you already have the class and can create instances from it, why do you need/want a Function object?

By: jackson

jackson — Fri, 23 Oct 2009 18:36:05 +0000

That’s not quite what I wanted to achieve. I want to be able to get a Function object that, when called, creates an instance of a class that I already have. If you know of a way of doing this other than my monstrous hack, please let me know.

By: Ben Clinkinbeard

Ben Clinkinbeard — Fri, 23 Oct 2009 18:18:19 +0000

If you already have a reference to the class, which your function requires, you can just use the new operator on it.

var c:Class = SomeClass;
var instance:SomeClass = new c( someArg, someOtherArg );

Does that do what you want or am I misunderstanding your goal?