Flash / Flex / ActionScript/Statement/as

Use as to check the object type

 
package{
  import flash.display.Sprite;
  
  public class Main extends Sprite{
    public function Main(){
        
        var checkout: Checkout = new Checkout();
        var d1:Didgeridoo = new Didgeridoo();
        var d2:Didgeridoo = new Didgeridoo();
        
        checkout.addItem(d1);
        checkout.addItem(d2);
        
        trace(checkout.calculate());
    }
  }
}

class Checkout {
    private var _items:Array;
    public function Checkout() {
      this._items = new Array();
    }
    public function addItem(product:IProduct):void {
      this._items.push(product);
    }
          public function calculate():uint {
      var tmp:uint = 0;
      for(var i:uint=0; i<this._items.length; i++) {
                    tmp += this._items[i].price;
        if(this._items[i] as ICustomizable != null) {
          if(this._items[i].customPrint != null) {
            tmp += 1;
          }
        }
      }
      return tmp;
    }
          
}
interface ICustomizable{
    function get customPrint():String;
    function set customPrint(s:String):void;
}
interface IProduct {
          function get price():uint;
          function set price(val:uint):void;
          function get name():String;
          function set name(val:String):void;
          function get description():String;
          function set description(val:String):void;
}
class Didgeridoo implements IProduct,ICustomizable {
    private var _price:uint = 100;
    private var _name:String = "Handpainted Didgeridoo";
    private var _description:String = "Imported from Australia";
    private var _customP:String = "No";
    
    public function get customPrint():String {
      return this._customP;
    }
    public function set customPrint(val:String):void {
      this._customP = val;
    }
    
    public function get price():uint {
      return this._price;
    }
    public function set price(val:uint):void {
      this._price = val;
    }
    public function get name():String {
      return this._name;
    }
    public function set name(val:String):void {
      this._name = val;
    }
    public function get description():String {
      return this._description;
    }
    public function set description(val:String):void {
      this._description = val;
    }
  }

Using the as Operator to Cast to Date and Array

 
package{
  import flash.display.Sprite;
  
  public class Main extends Sprite{
    public function Main(){
        var numbers:Array = [1,2,3]
        output(numbers);
    }
    public function output (msg:Object):void {
      if (msg is String) {
        trace(msg);
      }
    
      if (msg is Array) {
        var arr:Array = msg as Array;  // "Cast" to  Array  here    
        trace(arr.join("\n"));
      }
    }
  }
}