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      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 template<typename T>
    147 using RequireLongest = gdb::Requires<gdb::Or<std::is_same<T, LONGEST>,
    148 					     std::is_same<T, ULONGEST>>>;
    149 
    150 #endif /* COMMON_TRAITS_H */
    151