Eric Niebler <eric@boost-consulting.com> writes:
This is only a problem on GCC because of a compiler bug wrt template template parameters. Proto reuses a work-around from the MPL, which is conditioned on an MPL macro called BOOST_MPL_LIMIT_METAFUNCTION_ARITY. If you define this to be at least as large as BOOST_PROTO_MAX_ARITY, the problem goes away.
Mmmh, does the code I sent compile for you when ARITY==8? It still doesn't for me. (I get "ambiguous overload of operator OP", which is jargon for "your expression doesn't match the grammar") I've synched up and I see your change in matches.hpp for checking the proper settings of BOOST_MPL_LIMIT_METAFUNCTION_ARITY.
Also, in another mail, you say:
I'm really interested in having patterns with those many arguments, so once the variable controlling the maximum arity and the one controlling the maximum number of subpatterns in a pattern get decoupled I may be fine, but still giving a clear error message would be helpful.
Depending on what "number of subpatterns in a pattern" means, you may already have what you want. There is a separate macro called BOOST_PROTO_MAX_LOGICAL_ARITY which controls how many parameters proto::or_ and proto::and_ accept. It is independent of BOOST_PROTO_MAX_ARITY. For the time being, whether a pattern such as number<_,_,_,_,_,_,_,_> is accepted is controlled by BOOST_PROTO_MAX_ARITY.
I mean number<_,_,_,_,_,_,_,_>. I'll probably try to reduce the number of arguments by grouping even more of them in other structs, but for now I haven't come up with the right ones, which is why I prefer to have them lined up and do the grouping only once. Regards, Maurizio