Booleans - True, False, or Default

programming flash
1

I want a Boolean to have one one of three properties; true, false, or default.

Otherwise I need code like this in the getter/setter:

//WHAT I'M USING
private var _useTimestamp:Boolean;
private var _useTimestampDefault:Boolean;

public function get useTimestamp():Boolean
{
   if (_useTimeStampDefault)
      { return GlobalSettings.useTimestamp; }
   else
      { return _useTimestamp; }
}
public function set useTimestamp(value:Boolean)
{
   _useTimestampDefault = false;
   _useTimestamp = value;
}

public function get useTimestampDefault():Boolean
{
   return _useTimestampDefault;
}
public function set useTimestampDefault(value:Boolean)
{
   _useTimestampDefault = value;
}

This is what I want to do instead:

//What I want, A LOT less code
private var _useTimestamp:Boolean;

public function get useTimestamp():Boolean
{
   if (_useTimestamp == default)
      { return GlobalSettings.useTimestamp; }
   else
      { return _useTimestamp; }
}
public function set useTimestamp(value:Boolean)
{
   //Timestamp can be set to "true, false, or default/null"
   _useTimestamp = value;
}

Also, I want to use this feature as default values in properties

public function traceMe(str:String, useTimestamp:Boolean = GlobalSettings.useTimestamp)
{ ... }

But that throws the following error:
1047: Parameter initializer unknown or is not a compile-time constant.

I could create a new class that has one single property which handles boolean values, but that means that it is treated as an instance, and not as a real value, which means that statements like this might be off:
if (customBool) { … }

Is this possible? If I set the boolean to null, it will default to false, and that is not what I want.