ceph/src/boost/libs/hana/include/boost/hana/eval_if.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::eval_if`.
   4
   5 @copyright Louis Dionne 2013-2016
   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_EVAL_IF_HPP
  11 #define BOOST_HANA_EVAL_IF_HPP
  12
  13 #include <boost/hana/fwd/eval_if.hpp>
  14
  15 #include <boost/hana/bool.hpp>
  16 #include <boost/hana/concept/constant.hpp>
  17 #include <boost/hana/concept/logical.hpp>
  18 #include <boost/hana/config.hpp>
  19 #include <boost/hana/core/dispatch.hpp>
  20 #include <boost/hana/eval.hpp>
  21 #include <boost/hana/if.hpp>
  22
  23 #include <type_traits>
  24
  25
  26 BOOST_HANA_NAMESPACE_BEGIN
  27     //! @cond
  28     template <typename Cond, typename Then, typename Else>
  29     constexpr decltype(auto) eval_if_t::operator()(Cond&& cond, Then&& then, Else&& else_) const {
  30         using Bool = typename hana::tag_of<Cond>::type;
  31         using EvalIf = BOOST_HANA_DISPATCH_IF(eval_if_impl<Bool>,
  32             hana::Logical<Bool>::value
  33         );
  34
  35     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  36         static_assert(hana::Logical<Bool>::value,
  37         "hana::eval_if(cond, then, else) requires 'cond' to be a Logical");
  38     #endif
  39
  40         return EvalIf::apply(static_cast<Cond&&>(cond),
  41                              static_cast<Then&&>(then),
  42                              static_cast<Else&&>(else_));
  43     }
  44     //! @endcond
  45
  46     template <typename L, bool condition>
  47     struct eval_if_impl<L, when<condition>> : default_ {
  48         template <typename ...Args>
  49         static constexpr auto apply(Args&& ...) = delete;
  50     };
  51
  52     //////////////////////////////////////////////////////////////////////////
  53     // Model for arithmetic data types
  54     //////////////////////////////////////////////////////////////////////////
  55     template <typename L>
  56     struct eval_if_impl<L, when<std::is_arithmetic<L>::value>> {
  57         template <typename Cond, typename T, typename E>
  58         static constexpr auto apply(Cond const& cond, T&& t, E&& e) {
  59             return cond ? hana::eval(static_cast<T&&>(t))
  60                         : hana::eval(static_cast<E&&>(e));
  61         }
  62     };
  63
  64     //////////////////////////////////////////////////////////////////////////
  65     // Model for Constants over a Logical
  66     //////////////////////////////////////////////////////////////////////////
  67     template <typename C>
  68     struct eval_if_impl<C, when<
  69         hana::Constant<C>::value &&
  70         Logical<typename C::value_type>::value
  71     >> {
  72         template <typename Then, typename Else>
  73         static constexpr decltype(auto)
  74         eval_if_helper(hana::true_, Then&& t, Else&&)
  75         { return hana::eval(static_cast<Then&&>(t)); }
  76
  77         template <typename Then, typename Else>
  78         static constexpr decltype(auto)
  79         eval_if_helper(hana::false_, Then&&, Else&& e)
  80         { return hana::eval(static_cast<Else&&>(e)); }
  81
  82         template <typename Cond, typename Then, typename Else>
  83         static constexpr decltype(auto) apply(Cond const&, Then&& t, Else&& e) {
  84             constexpr auto cond = hana::value<Cond>();
  85             constexpr bool truth_value = hana::if_(cond, true, false);
  86             return eval_if_helper(hana::bool_c<truth_value>,
  87                                   static_cast<Then&&>(t),
  88                                   static_cast<Else&&>(e));
  89         }
  90     };
  91 BOOST_HANA_NAMESPACE_END
  92
  93 #endif // !BOOST_HANA_EVAL_IF_HPP