On Sun, Feb 1, 2009 at 7:10 AM, Robert Fraser <fraseroftheni...@gmail.com> wrote: > BCS wrote: >> >> Correct me if I'm wrong but I thing that D's opApply is a form of the >> Visitor pattern where the calling function's stack frame is the visitor >> object. >> >> This just occurred to me. Maybe I've been missing something re the visitor >> pattern but I think this make for a nice, cool and easy way to describe it. >> (Also I don't remember it being described that way) > > Er.... no. There's no double-dispatch (at least automatically), there's only > one foreach body delegate. The visitor pattern as far as I know it uses > dynamic dispatch so the visitor object can handle different objects in the > class hierarchy differently. For example, you couldn't use a foreach to > enumerate through a syntax tree and handle expressions and statements > differently (well, you could, but you'd have to do it manually).
I don't know/think that's a requirement for the actual visitor pattern to work. I think it's mostly that iteration is turned inside-out.
