Nagender Parimi <nkparimi@gmail.com> writes:
Hi,
I am looking for a static list of types, albeit one in which the order of types does not matter. I have looked into the Metaprogramming library (MPL) and some related work in BGL on property lists, but could not find anything that would make the list unordered (though they do provide a static type-list). To clarify what I mean, using the MPL:
typedef boost::mpl::vector<float, int> type1; typedef boost:mpl::vector<int, float> type2;
the above usage makes type1 and type2 distinct types since the ordering of types matters. Is there a library compenent with which I can construct a static list of types (just like usage of boost:mpl::vector above) and can query for presence or absence of a type, making the order irrelevant?
Furthermore, I would prefer this presence/absence check to be resolved compile-time. The reason for this requirement is that I wish to use this presence/absence test as means by which the compiler can call the appropriate specialized functions for this static list.
Sounds like a job for mpl::set. You can Instead of using mpl::equal, to check that two sets have the same elements you can use: // true iff s1 is a superset of s2 template <class s1, class s2> struct is_superset : boost::is_same< mpl::find_if< s1 , mpl::not_< mpl::has_key<s2,_> > >::type , mpl::end<s1>::type > {} mpl::and_< mpl::equal_to< mpl::size<s1> , mpl::size<s2> > , has_all<s1,s2>
::type
[Say, Aleksey, shouldn't contains<s,k> be a synonym for has_key<s,k> when s is a set? This example really makes me dream about Vesa's fully-lazy system. It's a bit annoying to have to write out is_superset as a separate metafunction.] -- Dave Abrahams Boost Consulting www.boost-consulting.com