libstdc++-v3/testsuite/20_util/variant/87619.cc

   1 // Copyright (C) 2018-2020 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-options "-std=gnu++17" }
  19 // { dg-do compile { target c++17 } }
  20
  21 #include <variant>
  22 #include <utility>
  23 #include <limits>
  24
  25 template<std::size_t I>
  26 struct S {
  27 };
  28
  29 template <std::size_t... Is>
  30 void f_impl(std::index_sequence<Is...>)
  31 {
  32         using V = std::variant<S<Is>...>;
  33         // For a variant of 255 alternatives the valid indices are [0,254]
  34         // and index 255 means valueless-by-exception, so fits in one byte.
  35         if constexpr (std::variant_size_v<V> <=
  36                       std::numeric_limits<unsigned char>::max())
  37           static_assert(sizeof(V) == 2);
  38         else
  39           static_assert(sizeof(V) > 2);
  40 }
  41
  42 template <std::size_t I>
  43 void f()
  44 {
  45         f_impl(std::make_index_sequence<I>{});
  46 }
  47
  48 int main()
  49 {
  50         f<std::numeric_limits<unsigned char>::max() - 1>();
  51         f<std::numeric_limits<unsigned char>::max()>();
  52         f<std::numeric_limits<unsigned char>::max() + 1>();
  53 }