ceph/src/boost/libs/hana/test/optional/nested_type.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/optional.hpp>
   6 #include <boost/hana/type.hpp>
   7
   8 #include <type_traits>
   9 namespace hana = boost::hana;
  10
  11
  12 // This test makes sure that an optional holding a hana::type has a
  13 // nested ::type alias.
  14
  15
  16 template <typename ...>
  17 using void_t = void;
  18
  19 template <typename T, typename = void>
  20 struct has_type : std::false_type { };
  21
  22 template <typename T>
  23 struct has_type<T, void_t<typename T::type>>
  24     : std::true_type
  25 { };
  26
  27
  28 struct T;
  29
  30 static_assert(std::is_same<decltype(hana::just(hana::type_c<T>))::type, T>{}, "");
  31 static_assert(!has_type<decltype(hana::nothing)>{}, "");
  32
  33 int main() { }