Difference Between Class Reference And Class Instance

Given that both of these calls to getQualifiedClassName return the same thing (mx:Label), how would one go about programatically differentiating between an instance of a class and a reference to the class...

    var lab1:Label=new Label();
    var lab2:Class=Label;
    var qcn1:String=getQual开发者_高级运维ifiedClassName(lab1);
    var qcn2:String=getQualifiedClassName(lab2);

In other words, how could I know that lab1 is of type Label, while lab2 is type "Class".

typeof() simply returns "object" for both... getQualifiedClassName returns "mx.controls::Label" for both...

What do I use?

The is operator:

>>> lab1 is Label
true
>>> lab1 is Class
false
>>> lab2 is Label
false
>>> lab2 is Class
true

Also (although this should be trivially true) lab2 == Label.

trace( Sprite is Class ); // true
trace( new Sprite() is Class ); // false

To test things in more details in the future, you can always use

import flash.utils.describeType;

trace(describeType(new Label()));
trace(describeType(Label));

This will give you 2 XML outputs. Here you will be able to clearly see the difference. I have provided 2 here for you for the Point class, since point is a relatively simple class compared to DisplayObjects and any class that extends off them.

Instance.

<type name="flash.geom::Point" base="Object" isDynamic="false" isFinal="false" isStatic="false">
  <extendsClass type="Object"/>
  <constructor>
    <parameter index="1" type="Number" optional="true"/>
    <parameter index="2" type="Number" optional="true"/>
  </constructor>
  <variable name="x" type="Number"/>
  <variable name="y" type="Number"/>
  <accessor name="length" access="readonly" type="Number" declaredBy="flash.geom::Point"/>
  <method name="clone" declaredBy="flash.geom::Point" returnType="flash.geom::Point"/>
  <method name="add" declaredBy="flash.geom::Point" returnType="flash.geom::Point">
    <parameter index="1" type="flash.geom::Point" optional="false"/>
  </method>
  <method name="equals" declaredBy="flash.geom::Point" returnType="Boolean">
    <parameter index="1" type="flash.geom::Point" optional="false"/>
  </method>
  <method name="subtract" declaredBy="flash.geom::Point" returnType="flash.geom::Point">
    <parameter index="1" type="flash.geom::Point" optional="false"/>
  </method>
  <method name="normalize" declaredBy="flash.geom::Point" returnType="void">
    <parameter index="1" type="Number" optional="false"/>
  </method>
  <method name="offset" declaredBy="flash.geom::Point" returnType="void">
    <parameter index="1" type="Number" optional="false"/>
    <parameter index="2" type="Number" optional="false"/>
  </method>
  <method name="toString" declaredBy="flash.geom::Point" returnType="String"/>
</type>

Class

<type name="flash.geom::Point" base="Class" isDynamic="true" isFinal="true" isStatic="true">
  <extendsClass type="Class"/>
  <extendsClass type="Object"/>
  <accessor name="prototype" access="readonly" type="*" declaredBy="Class"/>
  <method name="polar" declaredBy="flash.geom::Point" returnType="flash.geom::Point">
    <parameter index="1" type="Number" optional="false"/>
    <parameter index="2" type="Number" optional="false"/>
  </method>
  <method name="interpolate" declaredBy="flash.geom::Point" returnType="flash.geom::Point">
    <parameter index="1" type="flash.geom::Point" optional="false"/>
    <parameter index="2" type="flash.geom::Point" optional="false"/>
    <parameter index="3" type="Number" optional="false"/>
  </method>
  <method name="distance" declaredBy="flash.geom::Point" returnType="Number">
    <parameter index="1" type="flash.geom::Point" optional="false"/>
    <parameter index="2" type="flash.geom::Point" optional="false"/>
  </method>
  <factory type="flash.geom::Point">
    <extendsClass type="Object"/>
    <constructor>
      <parameter index="1" type="Number" optional="true"/>
      <parameter index="2" type="Number" optional="true"/>
    </constructor>
    <variable name="x" type="Number"/>
    <variable name="y" type="Number"/>
    <accessor name="length" access="readonly" type="Number" declaredBy="flash.geom::Point"/>
    <method name="clone" declaredBy="flash.geom::Point" returnType="flash.geom::Point"/>
    <method name="add" declaredBy="flash.geom::Point" returnType="flash.geom::Point">
      <parameter index="1" type="flash.geom::Point" optional="false"/>
    </method>
    <method name="equals" declaredBy="flash.geom::Point" returnType="Boolean">
      <parameter index="1" type="flash.geom::Point" optional="false"/>
    </method>
    <method name="subtract" declaredBy="flash.geom::Point" returnType="flash.geom::Point">
      <parameter index="1" type="flash.geom::Point" optional="false"/>
    </method>
    <method name="normalize" declaredBy="flash.geom::Point" returnType="void">
      <parameter index="1" type="Number" optional="false"/>
    </method>
    <method name="offset" declaredBy="flash.geom::Point" returnType="void">
      <parameter index="1" type="Number" optional="false"/>
      <parameter index="2" type="Number" optional="false"/>
    </method>
    <method name="toString" declaredBy="flash.geom::Point" returnType="String"/>
  </factory>
</type>

The Main differences being base="Object" and base="Class" and also the Class one has a <factory /> node. There are obviosuly more differences, but those are usually the parts I concentrate on the most.