Glad to hear that you found (or created) a solution. I would be very interested in seeing your re-worked Visitor, and Chandima is always interested in PureMVC.

So definitely ping back when you get a chance to write it up.

Kindest regards,
Bill

Any how I used a reworked implementation of the visitor to create channels of communication between a stack of loosely coupled pureMVC proxies, and it worked a treat.

If I get a chance to write it up, I’ll ping you back.

cheers, thanks for the resource, very hard to find AS3 implementations for many patterns

I see you’re using Java (no?) and a language called ‘Nice,’ and while we welcome insights and information from developers using other languages, the focus of our discussion is ActionScript 3.0 and Design Patterns using Adobe Flex Builder and Flash.

From a quick look at Nice, I cannot tell whether the role of multiple dispatch that apparently is built into Nice accomplishes exactly the same thing as the Visitor design pattern. While double dispatch is part of the Visitor, the key purpose of the Visitor is to add functionality (operations/methods/functionality) to components without changing the components–components in this case being any concrete class that makes up an element of a program.

In any case, thanks for your “Visit” to our blog.

Kindest regards,
Bill

http://nice.sourceforge.net/visitor.html

??

Perhaps the most useful way to distinguish between the Visitor and Decorator patterns is to begin with their general purposes and the aspects of the designs that can vary. The Decorator is a Structural pattern that can change the responsibilities of an object without subclassing. The Visitor is a Behavioral pattern that varies the operations that can be applied to objects without changing their classes. Structural object patterns describe ways to compose objects to realize new functionality instead of composing interfaces or implementations. The Decorator realizes the new functionality by wrapping objects with the functionality. The Visitor, on the other hand, encapsulates behavior that would otherwise be distributed across classes. As a Behavioral pattern, the Visitor focuses on algorithms and the assignment of responsibilities between objects. The big difference is that Behavioral object patterns (like the Visitor) use object composition rather than inheritance. But in looking at the Decorator, you see how it makes use of inheritance to compose interfaces and/or implementations.

In distinguishing between any design patterns, I always start with the larger categories (such as type) and look at the elements that vary. It’s an easy way to distinguish both the purpose and the approach to problem solving.

Kindest regards,
Bill

You may well be able to do the same thing with the Decorator,but what we’re trying to do is to provide a complete set of Design Patterns in ActionScript 3.0 between this blog and our book. (We’ve almost completed them all!)

In going over Chapter 4, I can see your point. The Decorator does indeed provide functionality to the component classes. The quick answer lies in the role of double-dispatch versus wrapping. The Visitor uses double-dispatch and the Decorator uses wrapping. However, let me look at both of them more closely and see if I can provide a better answer. (You can do the same! We’re a very democratic blog!)

Kindest regards,
Bill