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// { dg-do compile { target c++11 } }
// Copyright (C) 2014-2024 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
#include <tuple>
// A type that is contextually convertible to bool but cannot be used with
// the usual logical operators, and/or/not.
struct TwistedLogic {
bool value;
explicit operator bool() const noexcept { return value; }
};
template<typename T>
bool operator&&(const T&, TwistedLogic) = delete;
template<typename T>
bool operator&&(TwistedLogic, const T&) = delete;
template<typename T>
bool operator||(const T&, TwistedLogic) = delete;
template<typename T>
bool operator||(TwistedLogic, const T&) = delete;
bool operator!(TwistedLogic) noexcept = delete;
struct Compares {};
TwistedLogic operator==(const Compares&, const Compares&) { return {true}; }
TwistedLogic operator<(const Compares&, const Compares&) { return {false}; }
auto a = std::make_tuple(nullptr, Compares{}, 2, 'U');
auto b = a == a;
#if ! __cpp_lib_three_way_comparison
// Not valid in C++20, because TwistedLogic doesn't model boolean-testable.
auto c = std::make_tuple("", Compares{}, 2, 'U');
auto d = c < c;
#endif
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