ImmutableProxy.as

package {
import flash.errors.IllegalOperationError;
import flash.utils.Dictionary;
import flash.utils.Proxy;
import flash.utils.flash_proxy;

use namespace flash_proxy;
public dynamic class ImmutableProxy extends Proxy {
	private const propertyMap:Dictionary = new Dictionary();
	
	override flash_proxy function getProperty(name:*):* {
		return propertyMap[name];
	}
	
	override flash_proxy function setProperty(name:*, value:*):void {
		if (name in propertyMap) {
			throw new IllegalOperationError("Multiple mutation not supported.")
		}
		propertyMap[name] = value;
	}
	
}
}

ImmutableVO.as

package {

import flash.utils.flash_proxy;

use namespace flash_proxy;
class ImmutableVO extends ImmutableProxy {
	public function get property():* { 
		return flash_proxy::getProperty("property");
	}
	public function set property(value:*):void { 
		flash_proxy::setProperty("property", value);
	}
	
}
}