where can I find out about the visitor model
Adrian Crum sent the following on 11/26/2008 6:05 PM: > I would like to work on cleaning up the screen widget Java code. Here are > some of my ideas: > > 1. The screen widget model classes are trying to be too many things. As a > result, they contain some messy and scary code. I'd like to see the model > widget become more of a data structure, and move the rendering code into the > rendering classes. > > 2. Use a true visitor pattern in the model widgets. The current pattern is > what I would call "befuddled double dispatch with baggage." Methods like > > public void renderWidgetString(Appendable writer, Map<String, Object> > context, ScreenStringRenderer screenStringRenderer) > > would become > > public void accept(ScreenWidgetVisitor visitor). > > Rendering classes would implement the ScreenWidgetVisitor interface. The > model widgets won't need to be concerned with writers, contexts, or any other > messy details. > > 3. Convert the existing artifact gathering code to a screen widget visitor. > That would get the artifact gathering code out of the model widgets and put > it where it belongs. It would probably simplify the artifact gathering code > as well. > > Once these steps are completed, the model widget classes will be simple > immutable data structures. The only code most of the model classes will have > is a constructor and the accept method. > > The rendering code will be simplified, since there will be better separation > of concerns. > > I will probably start off with #1 - move the rendering code from the model > classes to the rendering classes. Once the dust settles from that, I will > introduce the visitor interfaces and visitor classes. The existing model > methods will be deprecated. The model classes will be bloated while they > support both patterns. When the time is right we can remove the deprecated > methods and we'll have lean, well structured screen widget code. > > What do you think? > > -Adrian > > > > > >
