gdbsupport/traits.h

   1 /* Copyright (C) 2017-2023 Free Software Foundation, Inc.
   2
   3    This file is part of GDB.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #ifndef COMMON_TRAITS_H
  19 #define COMMON_TRAITS_H
  20
  21 #include <type_traits>
  22
  23 /* GCC does not understand __has_feature.  */
  24 #if !defined(__has_feature)
  25 # define __has_feature(x) 0
  26 #endif
  27
  28 /* HAVE_IS_TRIVIALLY_COPYABLE is defined as 1 iff
  29    std::is_trivially_copyable is available.  GCC only implemented it
  30    in GCC 5.  */
  31 #if (__has_feature(is_trivially_copyable) \
  32      || (defined __GNUC__ && __GNUC__ >= 5))
  33 # define HAVE_IS_TRIVIALLY_COPYABLE 1
  34 #endif
  35
  36 /* HAVE_IS_TRIVIALLY_CONSTRUCTIBLE is defined as 1 iff
  37    std::is_trivially_constructible is available.  GCC only implemented it
  38    in GCC 5.  */
  39 #if (__has_feature(is_trivially_constructible) \
  40      || (defined __GNUC__ && __GNUC__ >= 5))
  41 # define HAVE_IS_TRIVIALLY_CONSTRUCTIBLE 1
  42 #endif
  43
  44 namespace gdb {
  45
  46 /* Implementation of the detection idiom:
  47
  48    - http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf
  49    - http://en.cppreference.com/w/cpp/experimental/is_detected
  50
  51 */
  52
  53 struct nonesuch
  54 {
  55   nonesuch () = delete;
  56   ~nonesuch () = delete;
  57   nonesuch (const nonesuch &) = delete;
  58   void operator= (const nonesuch &) = delete;
  59 };
  60
  61 namespace detection_detail {
  62 /* Implementation of the detection idiom (negative case).  */
  63 template<typename Default, typename AlwaysVoid,
  64          template<typename...> class Op, typename... Args>
  65 struct detector
  66 {
  67   using value_t = std::false_type;
  68   using type = Default;
  69 };
  70
  71 /* Implementation of the detection idiom (positive case).  */
  72 template<typename Default, template<typename...> class Op, typename... Args>
  73 struct detector<Default, std::void_t<Op<Args...>>, Op, Args...>
  74 {
  75   using value_t = std::true_type;
  76   using type = Op<Args...>;
  77 };
  78
  79 /* Detect whether Op<Args...> is a valid type, use Default if not.  */
  80 template<typename Default, template<typename...> class Op,
  81          typename... Args>
  82 using detected_or = detector<Default, void, Op, Args...>;
  83
  84 /* Op<Args...> if that is a valid type, otherwise Default.  */
  85 template<typename Default, template<typename...> class Op,
  86          typename... Args>
  87 using detected_or_t
  88   = typename detected_or<Default, Op, Args...>::type;
  89
  90 } /* detection_detail */
  91
  92 template<template<typename...> class Op, typename... Args>
  93 using is_detected
  94   = typename detection_detail::detector<nonesuch, void, Op, Args...>::value_t;
  95
  96 template<template<typename...> class Op, typename... Args>
  97 using detected_t
  98   = typename detection_detail::detector<nonesuch, void, Op, Args...>::type;
  99
 100 template<typename Default, template<typename...> class Op, typename... Args>
 101 using detected_or = detection_detail::detected_or<Default, Op, Args...>;
 102
 103 template<typename Default, template<typename...> class Op, typename... Args>
 104 using detected_or_t = typename detected_or<Default, Op, Args...>::type;
 105
 106 template<typename Expected, template<typename...> class Op, typename... Args>
 107 using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;
 108
 109 template<typename To, template<typename...> class Op, typename... Args>
 110 using is_detected_convertible
 111   = std::is_convertible<detected_t<Op, Args...>, To>;
 112
 113 /* A few trait helpers, mainly stolen from libstdc++.  Uppercase
 114    because "and/or", etc. are reserved keywords.  */
 115
 116 template<typename Predicate>
 117 struct Not : public std::integral_constant<bool, !Predicate::value>
 118 {};
 119
 120 template<typename...>
 121 struct Or;
 122
 123 template<>
 124 struct Or<> : public std::false_type
 125 {};
 126
 127 template<typename B1>
 128 struct Or<B1> : public B1
 129 {};
 130
 131 template<typename B1, typename B2>
 132 struct Or<B1, B2>
 133   : public std::conditional<B1::value, B1, B2>::type
 134 {};
 135
 136 template<typename B1,typename B2,typename B3, typename... Bn>
 137 struct Or<B1, B2, B3, Bn...>
 138   : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
 139 {};
 140
 141 template<typename...>
 142 struct And;
 143
 144 template<>
 145 struct And<> : public std::true_type
 146 {};
 147
 148 template<typename B1>
 149 struct And<B1> : public B1
 150 {};
 151
 152 template<typename B1, typename B2>
 153 struct And<B1, B2>
 154   : public std::conditional<B1::value, B2, B1>::type
 155 {};
 156
 157 template<typename B1, typename B2, typename B3, typename... Bn>
 158 struct And<B1, B2, B3, Bn...>
 159   : public std::conditional<B1::value, And<B2, B3, Bn...>, B1>::type
 160 {};
 161
 162 /* Concepts-light-like helper to make SFINAE logic easier to read.  */
 163 template<typename Condition>
 164 using Requires = typename std::enable_if<Condition::value, void>::type;
 165 }
 166
 167 #endif /* COMMON_TRAITS_H */