<aside> I bet for C++0x compilers that support SFINAE on expressions, we could build a much nicer Boost.ConceptCheck library. I'd be curious to see how far we could go. </aside>
You can go pretty far. I've been working on exactly this problem for the past week or so. I've basically taken the approach of treating requirements (i.e., of the form Iterator<X>) as a facade for type traits-style queries and Boost.ConceptCheck style-assertions (among other things). But, to address Dave's concerns:
a. I doubt we could do as well with error messages
You can't, but static_assert helps a bit.
b. It would be slower (at compile time)
It seems to be faster than ConceptGCC, but I agree that a compiler could do it better.
c. It wouldn't have the right syntax
Well, no. You can get close to "approximating" the syntax, but a real grammar would be better. Also, there are also some features that are essentially impossible to implement outside the compiler. Partially ordering overloads based on the most-refined model is one example.
d. It wouldn't do the right thing
What's the right thing, in this case? I have a couple of issues to work out, but I think I'll have a first draft of the library ready in the next day or so. I'll try to post a link and coherent introduction and overview then. Andrew Sutton andrew.n.sutton@gmail.com