Flash AS3: automate property assignment to new instance from arguments in constructor

Question

I like finding out about tricky new ways to do things. Let's say you've got a class with a property that gets set to the value of an argument in the constructor, like so:

package{
 public class SomeClass{
  private var someProperty:*;
  public function SomeClass(_someProperty:*):void{
   someProperty = _someProperty;
  }
 }
}

That's not exactly a hassle. But imagine you've got... I don't know, five properties. Ten properties, maybe. Rather then writing out each individual assignment, line by line, isn't there a way to loop through the constructor's arguments and set the value of each corresponding property on the new instance accordingly? I don't think that the ...rest or arguments objects will work, since they only keep an enumerated list of the arguments, not the argument names - I'm thinking something like this would be better:

for(var propertyName:String in argsAsAssocArray){this[propertyName] = argsAsAssocArray[propertyName];}

... does something like this exist?

It should be noted that the reason there's no built in way to do things like this is that (besides a few things like movieclips) objects don't have "names" in any real sense. If you define myFunction(str:String), then you get passed in a reference to a String, and that reference happens to be called "str", but the name "str" is not in any way a property of the String object in question. Hence if you use myFunction(..rest), then the objects that get passed in have no names at all! — fenomas
– fenomas, Commented Apr 9, 2010 at 12:37

Gama11 · Accepted Answer · 2019-03-10 14:10:59Z

1

No, there isn't. Here's what I use though:

class A {
    private var arg1:Type1;
    private var arg2:Type2;
    private var arg3:Type3;
    private var arg4:Type4;
    private static const PARAMS:Array = "arg1,arg2,arg3,arg4".split(",");
    public function A(arg1:Type1, arg2:Type2, arg3:Type3, arg4:Type4) {
        var i:uint = 0;
        for each (var name:String in PARAMS) this[name] = arguments[i++];
    }
}

You may want to check out Haxe. It has many advantages over AS3 and provides a solution even to this problem, using rtti, which unlike AS3 rtti also contains method parameter names.

edited Mar 10, 2019 at 14:10

Gama11

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answered Apr 9, 2010 at 8:55

back2dos

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1 Comment

Matt Lohkamp Over a year ago

it's just not possible, eh? I was kind of afraid of that. Oh well.

Theo.T · Accepted Answer · 2010-04-09 01:19:12Z

0

Using the reflection class describeType probably provides the most interesting information regarding the arguments, still unfortunately the property names aren't there either.

answered Apr 9, 2010 at 1:19

Theo.T

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