ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working with arrays
The following example defines a function named clone() that does deep copying. The algorithm is borrowed from a
common Java programming technique. The function creates a deep copy by serializing the array into an instance of
the ByteArray class, and then reading the array back into a new array. This function accepts an object so that it can be
used with both indexed arrays and associative arrays, as shown in the following code:
import flash.utils.ByteArray;
function clone(source:Object):*
{
var myBA:ByteArray = new ByteArray();
myBA.writeObject(source);
myBA.position = 0;
return(myBA.readObject());
}
Extending the Array class
Flash Player 9 and later, Adobe AIR 1.0 and later
The Array class is one of the few core classes that is not final, which means that you can create your own subclass of
Array. This section provides an example of how to create a subclass of Array and discusses some of the issues that can
arise during the process.
As mentioned previously, arrays in ActionScript are not typed, but you can create a subclass of Array that accepts
elements of only a specific data type. The example in the following sections defines an Array subclass named
TypedArray that limits its elements to values of the data type specified in the first parameter. The TypedArray class is
presented merely as an example of how to extend the Array class and may not be suitable for production purposes for
several reasons. First, type checking occurs at run time rather than at compile time. Second, when a TypedArray
method encounters a mismatch, the mismatch is ignored and no exception is thrown, although the methods can be
easily modified to throw exceptions. Third, the class cannot prevent the use of the array access operator to insert values
of any type into the array. Fourth, the coding style favors simplicity over performance optimization.
Note: You can use the technique described here to create a typed array. However, a better approach is to use a Vector
object. A Vector instance is a true typed array, and provides performance and other improvements over the Array class
or any subclass. The purpose of this discussion is to demonstrate how to create an Array subclass.
Declaring the subclass
Use the extends keyword to indicate that a class is a subclass of Array. A subclass of Array should use the dynamic
attribute, just as the Array class does. Otherwise, your subclass will not function properly.
The following code shows the definition of the TypedArray class, which contains a constant to hold the data type, a
constructor method, and the four methods that are capable of adding elements to the array. The code for each method
is omitted in this example, but is delineated and explained fully in the sections that follow:
Last updated 6/6/2012
43