libstdc++-v3/testsuite/20_util/allocator_traits/members/is_always_equal.cc

   1 // Copyright (C) 2015-2020 Free Software Foundation, Inc.
   2 //
   3 // This file is part of the GNU ISO C++ Library.  This library is free
   4 // software; you can redistribute it and/or modify it under the
   5 // terms of the GNU General Public License as published by the
   6 // Free Software Foundation; either version 3, or (at your option)
   7 // any later version.
   8
   9 // This library is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13
  14 // You should have received a copy of the GNU General Public License along
  15 // with this library; see the file COPYING3.  If not see
  16 // <http://www.gnu.org/licenses/>.
  17
  18 // { dg-do compile { target c++11 } }
  19
  20 #include <type_traits>
  21 #include <memory>
  22
  23 template<typename T, typename Base>
  24   struct Alloc : Base
  25   {
  26     typedef T value_type;
  27     Alloc();
  28     template <typename U>
  29       Alloc(const Alloc<U, Base>&);
  30     T* allocate(std::size_t);
  31     void deallocate(T*, std::size_t);
  32   };
  33
  34 template<bool> struct Empty { };
  35 template<> struct Empty<false> { int x; };
  36
  37 template<bool B>
  38   struct WithType
  39   { using is_always_equal = std::integral_constant<bool, B>; };
  40
  41 struct EmptyAndTrue : Empty<true>, WithType<true> { };
  42 struct EmptyButFalse : Empty<true>, WithType<false> { };
  43
  44 struct NotEmptyButTrue : Empty<false>, WithType<true> { };
  45 struct NotEmptyAndFalse : Empty<false>, WithType<false> { };
  46
  47 template<typename Base>
  48   constexpr bool test()
  49   {
  50     using traits = std::allocator_traits<Alloc<int, Base>>;
  51     using test_type = typename traits::is_always_equal;
  52     static_assert(std::is_base_of<std::true_type, test_type>::value
  53                   || std::is_base_of<std::false_type, test_type>::value,
  54                   "has correct base characteristic");
  55     return test_type::value;
  56   }
  57
  58 static_assert( test<Empty<true>>(), "empty type is always equal" );
  59 static_assert( !test<Empty<false>>(), "non-empty type is not always equal" );
  60
  61 static_assert( test<EmptyAndTrue>(), "nested type is used" );
  62 static_assert( !test<EmptyButFalse>(), "nested type is used" );
  63
  64 static_assert( test<NotEmptyButTrue>(), "nested type is used" );
  65 static_assert( !test<NotEmptyAndFalse>(), "nested type is used" );