gdbsupport/traits.h

   1 /* Copyright (C) 2017-2024 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 namespace gdb {
  24
  25 /* Implementation of the detection idiom:
  26
  27    - http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf
  28    - http://en.cppreference.com/w/cpp/experimental/is_detected
  29
  30 */
  31
  32 struct nonesuch
  33 {
  34   nonesuch () = delete;
  35   ~nonesuch () = delete;
  36   nonesuch (const nonesuch &) = delete;
  37   void operator= (const nonesuch &) = delete;
  38 };
  39
  40 namespace detection_detail {
  41 /* Implementation of the detection idiom (negative case).  */
  42 template<typename Default, typename AlwaysVoid,
  43          template<typename...> class Op, typename... Args>
  44 struct detector
  45 {
  46   using value_t = std::false_type;
  47   using type = Default;
  48 };
  49
  50 /* Implementation of the detection idiom (positive case).  */
  51 template<typename Default, template<typename...> class Op, typename... Args>
  52 struct detector<Default, std::void_t<Op<Args...>>, Op, Args...>
  53 {
  54   using value_t = std::true_type;
  55   using type = Op<Args...>;
  56 };
  57
  58 /* Detect whether Op<Args...> is a valid type, use Default if not.  */
  59 template<typename Default, template<typename...> class Op,
  60          typename... Args>
  61 using detected_or = detector<Default, void, Op, Args...>;
  62
  63 /* Op<Args...> if that is a valid type, otherwise Default.  */
  64 template<typename Default, template<typename...> class Op,
  65          typename... Args>
  66 using detected_or_t
  67   = typename detected_or<Default, Op, Args...>::type;
  68
  69 } /* detection_detail */
  70
  71 template<template<typename...> class Op, typename... Args>
  72 using is_detected
  73   = typename detection_detail::detector<nonesuch, void, Op, Args...>::value_t;
  74
  75 template<template<typename...> class Op, typename... Args>
  76 using detected_t
  77   = typename detection_detail::detector<nonesuch, void, Op, Args...>::type;
  78
  79 template<typename Default, template<typename...> class Op, typename... Args>
  80 using detected_or = detection_detail::detected_or<Default, Op, Args...>;
  81
  82 template<typename Default, template<typename...> class Op, typename... Args>
  83 using detected_or_t = typename detected_or<Default, Op, Args...>::type;
  84
  85 template<typename Expected, template<typename...> class Op, typename... Args>
  86 using is_detected_exact = std::is_same<Expected, detected_t<Op, Args...>>;
  87
  88 template<typename To, template<typename...> class Op, typename... Args>
  89 using is_detected_convertible
  90   = std::is_convertible<detected_t<Op, Args...>, To>;
  91
  92 /* A few trait helpers, mainly stolen from libstdc++.  Uppercase
  93    because "and/or", etc. are reserved keywords.  */
  94
  95 template<typename Predicate>
  96 struct Not : public std::integral_constant<bool, !Predicate::value>
  97 {};
  98
  99 template<typename...>
 100 struct Or;
 101
 102 template<>
 103 struct Or<> : public std::false_type
 104 {};
 105
 106 template<typename B1>
 107 struct Or<B1> : public B1
 108 {};
 109
 110 template<typename B1, typename B2>
 111 struct Or<B1, B2>
 112   : public std::conditional<B1::value, B1, B2>::type
 113 {};
 114
 115 template<typename B1,typename B2,typename B3, typename... Bn>
 116 struct Or<B1, B2, B3, Bn...>
 117   : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
 118 {};
 119
 120 template<typename...>
 121 struct And;
 122
 123 template<>
 124 struct And<> : public std::true_type
 125 {};
 126
 127 template<typename B1>
 128 struct And<B1> : public B1
 129 {};
 130
 131 template<typename B1, typename B2>
 132 struct And<B1, B2>
 133   : public std::conditional<B1::value, B2, B1>::type
 134 {};
 135
 136 template<typename B1, typename B2, typename B3, typename... Bn>
 137 struct And<B1, B2, B3, Bn...>
 138   : public std::conditional<B1::value, And<B2, B3, Bn...>, B1>::type
 139 {};
 140
 141 /* Concepts-light-like helper to make SFINAE logic easier to read.  */
 142 template<typename Condition>
 143 using Requires = typename std::enable_if<Condition::value, void>::type;
 144 }
 145
 146 #endif /* COMMON_TRAITS_H */