ceph/src/boost/libs/hana/example/type/is_valid.cpp

   1 // Copyright Louis Dionne 2013-2016
   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/not.hpp>
   7 #include <boost/hana/type.hpp>
   8
   9 #include <string>
  10 #include <vector>
  11 namespace hana = boost::hana;
  12
  13
  14 int main() {
  15     // Checking for a member
  16     struct Person { std::string name; };
  17     auto has_name = hana::is_valid([](auto&& p) -> decltype((void)p.name) { });
  18
  19     Person joe{"Joe"};
  20     static_assert(has_name(joe), "");
  21     static_assert(!has_name(1), "");
  22
  23
  24     // Checking for a nested type
  25     auto has_value_type = hana::is_valid([](auto t) -> hana::type<
  26         typename decltype(t)::type::value_type
  27     > { });
  28
  29     static_assert(has_value_type(hana::type_c<std::vector<int>>), "");
  30     static_assert(!has_value_type(hana::type_c<Person>), "");
  31 }