ceph/src/boost/libs/hana/test/concept/integral_constant.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/concept/constant.hpp>
   6 #include <boost/hana/concept/integral_constant.hpp>
   7 #include <boost/hana/core/when.hpp>
   8 #include <boost/hana/fwd/core/to.hpp>
   9 #include <boost/hana/value.hpp>
  10 namespace hana = boost::hana;
  11
  12
  13 // Define a simple model of IntegralConstant
  14 struct constant_tag { using value_type = int; };
  15 template <int i>
  16 struct constant {
  17     static constexpr int value = i;
  18     using hana_tag = constant_tag;
  19 };
  20
  21 namespace boost { namespace hana {
  22     template <>
  23     struct IntegralConstant<constant_tag> {
  24         static constexpr bool value = true;
  25     };
  26
  27     template <typename From>
  28     struct to_impl<constant_tag, From, when<IntegralConstant<From>::value>> {
  29         template <typename N>
  30         static constexpr auto apply(N const&)
  31         { return constant<N::value>{}; }
  32     };
  33 }}
  34
  35 // Make sure we really satisfy IntegralConstant<>.
  36 static_assert(hana::IntegralConstant<constant<0>>::value, "");
  37 static_assert(hana::IntegralConstant<constant<1>>::value, "");
  38 static_assert(hana::IntegralConstant<constant<2>>::value, "");
  39
  40 // Make sure we're also a model of Constant automatically.
  41 static_assert(hana::Constant<constant<0>>::value, "");
  42 static_assert(hana::Constant<constant<1>>::value, "");
  43 static_assert(hana::Constant<constant<2>>::value, "");
  44
  45 // Make sure we have the hana::value<> function defined automatically.
  46 static_assert(hana::value<constant<0>>() == 0, "");
  47 static_assert(hana::value<constant<1>>() == 1, "");
  48 static_assert(hana::value<constant<2>>() == 2, "");
  49 static_assert(hana::value<constant<3>>() == 3, "");
  50
  51
  52 int main() { }