54 lines
1.6 KiB
C++
54 lines
1.6 KiB
C++
// Copyright (C) 2018-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-options "-std=gnu++17" }
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// { dg-do compile { target c++17 } }
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#include <variant>
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#include <utility>
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#include <limits>
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template<std::size_t I>
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struct S {
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};
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template <std::size_t... Is>
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void f_impl(std::index_sequence<Is...>)
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{
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using V = std::variant<S<Is>...>;
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// For a variant of 255 alternatives the valid indices are [0,254]
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// and index 255 means valueless-by-exception, so fits in one byte.
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if constexpr (std::variant_size_v<V> <=
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std::numeric_limits<unsigned char>::max())
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static_assert(sizeof(V) == 2);
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else
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static_assert(sizeof(V) > 2);
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}
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template <std::size_t I>
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void f()
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{
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f_impl(std::make_index_sequence<I>{});
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}
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int main()
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{
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f<std::numeric_limits<unsigned char>::max() - 1>();
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f<std::numeric_limits<unsigned char>::max()>();
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f<std::numeric_limits<unsigned char>::max() + 1>();
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}
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