actionscript: undefined public variables??

Question

I have a class like this..

public class Doc {
  public function Doc():void {}

  public var myVar:Boolean;
}

How can I know if the value hold by myVar is the default false, or someone has assigned false to it ?!? Isn't there an undefined state? How can I achieve such a thing?

Answer 1

Make myVar a property and use another variable to check if it's been set explicitly.

public class Doc 
{
  public function Doc():void {}

  private var _myVar:Boolean;
  private var myVarSetExplicitly:Boolean = false;
  public function get myVar():Boolean
  {
    return _myVar;
  }
  public function set myVar(value:Boolean):void
  {
    myVarSetExplicitly = true;
    _myVar = value;
  }
}

Answer 2

You can't with a boolean, it defaults to false and false === false.

You'd could not strictly type the variable and then use a getter and setter to protect the type

public class Doc {
  private var _myVar;

  public function set myVar(value:Boolean){
    _myVar = value;
  }

  public function get myVar(){
    return _myVar;
  }
}

Now, when its not set myVar should === null, and you should only be able to set it to a boolean after that.

But it feels a bit hacky, and I wonder why you need to tell the difference.