ceph/src/boost/boost/hana/ext/std/integral_constant.hpp

   1 /*!
   2 @file
   3 Adapts `std::integral_constant` for use with Hana.
   4
   5 @copyright Louis Dionne 2013-2017
   6 Distributed under the Boost Software License, Version 1.0.
   7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   8  */
   9
  10 #ifndef BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP
  11 #define BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP
  12
  13 #include <boost/hana/concept/integral_constant.hpp>
  14 #include <boost/hana/config.hpp>
  15 #include <boost/hana/core/when.hpp>
  16 #include <boost/hana/fwd/core/to.hpp>
  17 #include <boost/hana/fwd/core/tag_of.hpp>
  18 #include <boost/hana/fwd/integral_constant.hpp>
  19
  20 #include <type_traits>
  21
  22
  23 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  24 namespace std {
  25     //! @ingroup group-ext-std
  26     //! Adapter for `std::integral_constant`s.
  27     //!
  28     //! Provided models
  29     //! ---------------
  30     //! 1. `Constant` and `IntegralConstant`\n
  31     //! A `std::integral_constant` is a model of the `IntegralConstant` and
  32     //! `Constant` concepts, just like `hana::integral_constant`s are. As a
  33     //! consequence, they are also implicitly a model of the concepts provided
  34     //! for all models of `Constant`.
  35     //! @include example/ext/std/integral_constant.cpp
  36     template <typename T, T v>
  37     struct integral_constant { };
  38 }
  39 #endif
  40
  41
  42 BOOST_HANA_NAMESPACE_BEGIN
  43     namespace ext { namespace std {
  44         template <typename T>
  45         struct integral_constant_tag { using value_type = T; };
  46     }}
  47
  48     namespace detail {
  49         template <typename T, T v>
  50         constexpr bool
  51         is_std_integral_constant(std::integral_constant<T, v>*)
  52         { return true; }
  53
  54         constexpr bool is_std_integral_constant(...)
  55         { return false; }
  56
  57
  58         template <typename T, T v>
  59         constexpr bool
  60         is_hana_integral_constant(hana::integral_constant<T, v>*)
  61         { return true; }
  62
  63         constexpr bool is_hana_integral_constant(...)
  64         { return false; }
  65     }
  66
  67     template <typename T>
  68     struct tag_of<T, when<
  69         detail::is_std_integral_constant((T*)0) &&
  70         !detail::is_hana_integral_constant((T*)0)
  71     >> {
  72         using type = ext::std::integral_constant_tag<
  73             typename hana::tag_of<typename T::value_type>::type
  74         >;
  75     };
  76
  77     //////////////////////////////////////////////////////////////////////////
  78     // Constant/IntegralConstant
  79     //////////////////////////////////////////////////////////////////////////
  80     template <typename T>
  81     struct IntegralConstant<ext::std::integral_constant_tag<T>> {
  82         static constexpr bool value = true;
  83     };
  84
  85     template <typename T, typename C>
  86     struct to_impl<ext::std::integral_constant_tag<T>, C, when<
  87         hana::IntegralConstant<C>::value
  88     >> : embedding<is_embedded<typename C::value_type, T>::value> {
  89         template <typename N>
  90         static constexpr auto apply(N const&) {
  91             return std::integral_constant<T, N::value>{};
  92         }
  93     };
  94 BOOST_HANA_NAMESPACE_END
  95
  96 #endif // !BOOST_HANA_EXT_STD_INTEGRAL_CONSTANT_HPP