800 Object-Oriented Programming with ActionScript 1.0
Adding getter/setter properties to objects
in ActionScript 1.0
You can create getter/setter properties for an object using the Object.addProperty()
method.
A getter function is a function with no parameters. Its return value can be of any type. Its
type can change between invocations. The return value is treated as the current value of
the property.
A setter function is a function that takes one parameter, which is the new value of the property.
For instance, if property x is assigned by the statement x = 1, the setter function is passed the
parameter 1 of type Number. The return value of the setter function is ignored.
When Flash reads a getter/setter property, it invokes the getter function, and the function’s
return value becomes a value of
prop. When Flash writes a getter/setter property, it invokes
the setter function and passes it the new value as a parameter. If a property with the given
name already exists, the new property overwrites it.
You can add getter/setter properties to prototype objects. If you add a getter/setter property to
a prototype object, all object instances that inherit the prototype object inherit the getter/
setter property. You can add a getter/setter property in one location, the prototype object, and
have it propagate to all instances of a class (similar to adding methods to prototype objects). If
a getter/setter function is invoked for a getter/setter property in an inherited prototype object,
the reference passed to the getter/setter function is the originally referenced object, not the
prototype object.
The Debug > List Variables command in test mode supports getter/setter properties that you
add to objects using
Object.addProperty(). Properties that you add to an object in this way
appear with other properties of the object in the Output panel. Getter/setter properties are
identified in the Output panel with the prefix
[getter/setter]. For more information on
the List Variables command, see “Using the Output panel” on page 724.
NOTE
Many Flash users can greatly benefit from using ActionScript 2.0, especially with
complex applications. For information on using ActionScript 2.0, see Chapter 7,
“Classes,” on page 225.
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