1 // Copyright Louis Dionne 2013-2017
2 // Distributed under the Boost Software License, Version 1.0.
3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
4
5 #include <boost/hana/assert.hpp>
6 #include <boost/hana/equal.hpp>
7 #include <boost/hana/hash.hpp>
8 #include <boost/hana/integral_constant.hpp>
9 #include <boost/hana/type.hpp>
10
11 #include <type_traits>
12 #include <utility>
13 namespace hana = boost::hana;
14
15
16 // Sample implementation of a compile-time set data structure. Of course,
17 // this naive implementation only works when no two elements of the same
18 // set have the same hash.
19 template <typename T>
20 struct bucket { };
21
22 template <typename ...T>
23 struct set
24 : bucket<typename decltype(hana::hash(std::declval<T>()))::type>...
25 { };
26
27 template <typename Set, typename T>
28 struct contains
29 : std::is_base_of<
30 bucket<typename decltype(hana::hash(std::declval<T>()))::type>,
31 Set
32 >
33 { };
34
35 using Set = set<hana::int_<1>, hana::ulong<2>, hana::type<char>>;
36
37 static_assert(contains<Set, hana::int_<1>>{}, "");
38 static_assert(contains<Set, hana::ulong<2>>{}, "");
39 static_assert(contains<Set, hana::type<char>>{}, "");
40
41 static_assert(!contains<Set, hana::int_<3>>{}, "");
42 static_assert(!contains<Set, hana::type<float>>{}, "");
43
main()44 int main() { }
45