On May 29, 2011, at 6:05 PM, Robert Ramey wrote:
Expression Requirments ====================== next(i) ...
Meta Expressions ============ result_of::next<I>::type ...
Expression Semantics =============== next(i) - An iterator to the element following i ...
So the quesion is: Why is result_of::next<I>::type necessary? The expression symantics only make sense if next(i) if it returns the same type as it's argument. So why is the result_of::next<I>::type needed at all. That is won't it always be equal to I. If not, why not?
That's exactly it - Fusion has compile-time heterogeneous sequences, so the elements will probably be of different types, and the incremented iterator is always of a different type. This is something I need too, as I'm working on the proposed Fusion.Graph, so I need to define BGL-like concepts on top of Fusion concepts. I imagine you would look at how concepts are defined for metafunctions; I haven't looked at the Concept Check library. (Hoping that Matt Calabrese's proposed Boost.Generic will be up and running later this year!) Cheers, Gordon