gdbsupport/traits.h

   1 /* Copyright (C) 2017-2022 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 /* Pre C++14-safe (CWG 1558) version of C++17's std::void_t.  See
  47    <http://en.cppreference.com/w/cpp/types/void_t>.  */
  48
  49 template<typename... Ts>
  50 struct make_void { typedef void type; };
  51
  52 template<typename... Ts>
  53 using void_t = typename make_void<Ts...>::type;
  54
  55 /* Implementation of the detection idiom:
  56
  57    - http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf
  58    - http://en.cppreference.com/w/cpp/experimental/is_detected
  59
  60 */
  61
  62 struct nonesuch
  63 {
  64   nonesuch () = delete;
  65   ~nonesuch () = delete;
  66   nonesuch (const nonesuch &) = delete;
  67   void operator= (const nonesuch &) = delete;
  68 };
  69
  70 namespace detection_detail {
  71 /* Implementation of the detection idiom (negative case).  */
  72 template<typename Default, typename AlwaysVoid,
  73          template<typename...> class Op, typename... Args>
  74 struct detector
  75 {
  76   using value_t = std::false_type;
  77   using type = Default;
  78 };
  79
  80 /* Implementation of the detection idiom (positive case).  */
  81 template<typename Default, template<typename...> class Op, typename... Args>
  82 struct detector<Default, void_t<Op<Args...>>, Op, Args...>
  83 {
  84   using value_t = std::true_type;
  85   using type = Op<Args...>;
  86 };
  87
  88 /* Detect whether Op<Args...> is a valid type, use Default if not.  */
  89 template<typename Default, template<typename...> class Op,
  90          typename... Args>
  91 using detected_or = detector<Default, void, Op, Args...>;
  92
  93 /* Op<Args...> if that is a valid type, otherwise Default.  */
  94 template<typename Default, template<typename...> class Op,
  95          typename... Args>
  96 using detected_or_t
  97   = typename detected_or<Default, Op, Args...>::type;
  98
  99 } /* detection_detail */
 100
 101 template<template<typename...> class Op, typename... Args>
 102 using is_detected
 103   = typename detection_detail::detector<nonesuch, void, Op, Args...>::value_t;
 104
 105 template<template<typename...> class Op, typename... Args>
 106 using detected_t
 107   = typename detection_detail::detector<nonesuch, void, Op, Args...>::type;
 108
 109 template<typename Default, template<typename...> class Op, typename... Args>
 110 using detected_or = detection_detail::detected_or<Default, Op, Args...>;
 111
 112 template<typename Default, template<typename...> class Op, typename... Args>
 113 using detected_or_t = typename detected_or<Default, Op, Args...>::type;
 114
 115 template<typename Expected, template<typename...> class Op, typename... Args>
 116 using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;
 117
 118 template<typename To, template<typename...> class Op, typename... Args>
 119 using is_detected_convertible
 120   = std::is_convertible<detected_t<Op, Args...>, To>;
 121
 122 /* A few trait helpers, mainly stolen from libstdc++.  Uppercase
 123    because "and/or", etc. are reserved keywords.  */
 124
 125 template<typename Predicate>
 126 struct Not : public std::integral_constant<bool, !Predicate::value>
 127 {};
 128
 129 template<typename...>
 130 struct Or;
 131
 132 template<>
 133 struct Or<> : public std::false_type
 134 {};
 135
 136 template<typename B1>
 137 struct Or<B1> : public B1
 138 {};
 139
 140 template<typename B1, typename B2>
 141 struct Or<B1, B2>
 142   : public std::conditional<B1::value, B1, B2>::type
 143 {};
 144
 145 template<typename B1,typename B2,typename B3, typename... Bn>
 146 struct Or<B1, B2, B3, Bn...>
 147   : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
 148 {};
 149
 150 template<typename...>
 151 struct And;
 152
 153 template<>
 154 struct And<> : public std::true_type
 155 {};
 156
 157 template<typename B1>
 158 struct And<B1> : public B1
 159 {};
 160
 161 template<typename B1, typename B2>
 162 struct And<B1, B2>
 163   : public std::conditional<B1::value, B2, B1>::type
 164 {};
 165
 166 template<typename B1, typename B2, typename B3, typename... Bn>
 167 struct And<B1, B2, B3, Bn...>
 168   : public std::conditional<B1::value, And<B2, B3, Bn...>, B1>::type
 169 {};
 170
 171 /* Concepts-light-like helper to make SFINAE logic easier to read.  */
 172 template<typename Condition>
 173 using Requires = typename std::enable_if<Condition::value, void>::type;
 174 }
 175
 176 #endif /* COMMON_TRAITS_H */