On 10/21/10 11:11 AM, Eric Niebler wrote:
On 10/20/2010 7:49 AM, Thomas Heller wrote:
I worked a little on trying to simplify that whole grammar with
rules that have thing a bit. Forgive me, but i changed the name to Visitor.
Why? Simply because i think this is what is done here. We visit a specific
node which happened to match our rule.
Most tree traversal algorithms "visit" each node, but the term "Visitor"
means something very, very specific: the Gang-of-Four Visitor Design
Pattern. It implies an OO hierarchy, a virtual "Dispatch" member that
accepts a visitor, and a 2nd dispatch to an "Accept" member of the
visitor object. It is used to "add" members to an OO hierarchy post-hoc
by putting them in a visitor instead of having to change every type in
your hierarchy.
If you don't have something like that, then don't call it Visitor. If
you do, then we need to reformulate this design to make that pattern
more explicit. Otherwise, it will cause no end of confusion.
Historical note: I originally called the "data" parameter of Proto
transforms "visitors". During the review, there was such a hue and cry
(for good reason) that I had to change it. True story.
Do you mean that it has to be exactly that to be called a "visitor"?
How exact? Does it have to be "an OO hierarchy with a virtual "Dispatch"
member that accepts a visitor"?
Does the Boost Variant visitation scheme (for example) satisfy these
conditions?
Regards,
--
Joel de Guzman
http://www.boostpro.com
http://spirit.sf.net
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