ceph/src/boost/boost/hana/one.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::one`.
   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_ONE_HPP
  11 #define BOOST_HANA_ONE_HPP
  12
  13 #include <boost/hana/fwd/one.hpp>
  14
  15 #include <boost/hana/concept/constant.hpp>
  16 #include <boost/hana/concept/ring.hpp>
  17 #include <boost/hana/config.hpp>
  18 #include <boost/hana/core/to.hpp>
  19 #include <boost/hana/core/dispatch.hpp>
  20 #include <boost/hana/detail/canonical_constant.hpp>
  21
  22 #include <type_traits>
  23
  24
  25 BOOST_HANA_NAMESPACE_BEGIN
  26     template <typename R>
  27     struct one_t {
  28     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  29         static_assert(hana::Ring<R>::value,
  30         "hana::one<R>() requires 'R' to be a Ring");
  31     #endif
  32
  33         constexpr decltype(auto) operator()() const {
  34             using One = BOOST_HANA_DISPATCH_IF(one_impl<R>,
  35                 hana::Ring<R>::value
  36             );
  37
  38             return One::apply();
  39         }
  40     };
  41
  42     template <typename R, bool condition>
  43     struct one_impl<R, when<condition>> : default_ {
  44         template <typename ...Args>
  45         static constexpr auto apply(Args&& ...) = delete;
  46     };
  47
  48     //////////////////////////////////////////////////////////////////////////
  49     // Model for non-boolean arithmetic data types
  50     //////////////////////////////////////////////////////////////////////////
  51     template <typename T>
  52     struct one_impl<T, when<std::is_arithmetic<T>::value &&
  53                             !std::is_same<bool, T>::value>> {
  54         static constexpr T apply()
  55         { return static_cast<T>(1); }
  56     };
  57
  58     //////////////////////////////////////////////////////////////////////////
  59     // Model for Constants over a Ring
  60     //////////////////////////////////////////////////////////////////////////
  61     namespace detail {
  62         template <typename C>
  63         struct constant_from_one {
  64             static constexpr auto value = hana::one<typename C::value_type>();
  65             using hana_tag = detail::CanonicalConstant<typename C::value_type>;
  66         };
  67     }
  68
  69     template <typename C>
  70     struct one_impl<C, when<
  71         hana::Constant<C>::value &&
  72         Ring<typename C::value_type>::value
  73     >> {
  74         static constexpr decltype(auto) apply()
  75         { return hana::to<C>(detail::constant_from_one<C>{}); }
  76     };
  77 BOOST_HANA_NAMESPACE_END
  78
  79 #endif // !BOOST_HANA_ONE_HPP