gdb/common/traits.h

   1 /* Copyright (C) 2017 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 /* Pre C++14-safe (CWG 1558) version of C++17's std::void_t.  See
  26    <http://en.cppreference.com/w/cpp/types/void_t>.  */
  27
  28 template<typename... Ts>
  29 struct make_void { typedef void type; };
  30
  31 template<typename... Ts>
  32 using void_t = typename make_void<Ts...>::type;
  33
  34 /* A few trait helpers, mainly stolen from libstdc++.  Uppercase
  35    because "and/or", etc. are reserved keywords.  */
  36
  37 template<typename Predicate>
  38 struct Not : public std::integral_constant<bool, !Predicate::value>
  39 {};
  40
  41 template<typename...>
  42 struct Or;
  43
  44 template<>
  45 struct Or<> : public std::false_type
  46 {};
  47
  48 template<typename B1>
  49 struct Or<B1> : public B1
  50 {};
  51
  52 template<typename B1, typename B2>
  53 struct Or<B1, B2>
  54   : public std::conditional<B1::value, B1, B2>::type
  55 {};
  56
  57 template<typename B1,typename B2,typename B3, typename... Bn>
  58 struct Or<B1, B2, B3, Bn...>
  59   : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
  60 {};
  61
  62 template<typename...>
  63 struct And;
  64
  65 template<>
  66 struct And<> : public std::true_type
  67 {};
  68
  69 template<typename B1>
  70 struct And<B1> : public B1
  71 {};
  72
  73 template<typename B1, typename B2>
  74 struct And<B1, B2>
  75   : public std::conditional<B1::value, B2, B1>::type
  76 {};
  77
  78 template<typename B1, typename B2, typename B3, typename... Bn>
  79 struct And<B1, B2, B3, Bn...>
  80   : public std::conditional<B1::value, And<B2, B3, Bn...>, B1>::type
  81 {};
  82
  83 /* Concepts-light-like helper to make SFINAE logic easier to read.  */
  84 template<typename Condition>
  85 using Requires = typename std::enable_if<Condition::value, void>::type;
  86 }
  87
  88 #endif /* COMMON_TRAITS_H */