Daniel Earwicker <daniel.earwicker@gmail.com> writes:
Oooh, that's much better. With used_keywords as an empty set in empty_arg_list, all it needs in arg_list is:
BOOST_STATIC_ASSERT((!boost::mpl::has_key< typename Next::used_keywords, key_type>::type::value));
Use BOOST_MPL_ASSERT_MSG here.
typedef typename mpl::insert<typename Next::used_keywords, key_type>::type used_keywords;
Or is there already something that captures the above pattern, i.e. refuses to insert a duplicate?
Not that I know of. Actually in this case I think I'd prefer to see a solution using overloading directly, just to cut down on instantiations. The arg_list, after all, is almost the same structure as the set already. Something like: static char (& has_key(K const&) )[2]; BOOST_MPL_ASSERT_MSG( sizeof(Next::has_key(make<K>())) == 1 , duplicate_keyword, (K) ); If you could submit a patch to the current CVS along with an expected-compilation-failure test case, I'd be happy to apply it. -- Dave Abrahams Boost Consulting www.boost-consulting.com