ceph/src/boost/boost/hof/detail/constexpr_deduce.hpp

   1 /*=============================================================================
   2     Copyright (c) 2015 Paul Fultz II
   3     constexpr_deduce.h
   4     Distributed under the Boost Software License, Version 1.0. (See accompanying
   5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 ==============================================================================*/
   7
   8 #ifndef BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H
   9 #define BOOST_HOF_GUARD_FUNCTION_CONSTEXPR_DEDUCE_H
  10
  11 #include <boost/hof/config.hpp>
  12
  13 #define BOOST_HOF_CONST_FOLD(x) (__builtin_constant_p(x) ? (x) : (x))
  14
  15 #ifndef BOOST_HOF_HAS_CONST_FOLD
  16 #if defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7
  17 #define BOOST_HOF_HAS_CONST_FOLD 0
  18 #elif defined(__clang__) || defined (__GNUC__)
  19 #define BOOST_HOF_HAS_CONST_FOLD 1
  20 #else
  21 #define BOOST_HOF_HAS_CONST_FOLD 0
  22 #endif
  23 #endif
  24
  25
  26 namespace boost { namespace hof {
  27
  28 namespace detail {
  29
  30 struct constexpr_deduce
  31 {
  32     constexpr constexpr_deduce()
  33     {}
  34     template<class F>
  35     constexpr operator F() const
  36     {
  37         return F();
  38     }
  39 };
  40
  41 template<class T>
  42 struct constexpr_deduce_unique
  43 {
  44     constexpr constexpr_deduce_unique()
  45     {}
  46 #if BOOST_HOF_HAS_CONST_FOLD
  47     template<class F>
  48     constexpr operator const F&() const
  49     {
  50         static_assert(BOOST_HOF_IS_EMPTY(F), "Function or lambda expression must be empty");
  51         return BOOST_HOF_CONST_FOLD(reinterpret_cast<const F&>(static_const_var<T>()));
  52     }
  53 #else
  54     template<class F>
  55     constexpr operator F() const
  56     {
  57         // static_assert(std::is_default_constructible<F>::value, "Function not default constructible");
  58         return F();
  59     }
  60 #endif
  61 };
  62
  63 }}} // namespace boost::hof
  64
  65 #define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE true ? boost::hof::detail::constexpr_deduce() :
  66 #define BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE_UNIQUE(T) true ? boost::hof::detail::constexpr_deduce_unique<T>() :
  67
  68 #ifdef _MSC_VER
  69 #define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE BOOST_HOF_DETAIL_CONSTEXPR_DEDUCE
  70 #else
  71 #define BOOST_HOF_DETAIL_MSVC_CONSTEXPR_DEDUCE
  72 #endif
  73
  74 #endif