ceph/src/boost/libs/hana/example/hash.cpp

   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
  44 int main() { }