//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++98, c++03, c++11, c++14
// <optional>

// template <class T, class U> constexpr bool operator< (const optional<T>& x, const optional<U>& y);

#include <optional>

using std::optional;

struct X {
  int i_;

  constexpr X(int i) : i_(i) {}
};

constexpr bool operator<(const X& lhs, const X& rhs) { return lhs.i_ < rhs.i_; }

int main(int, char**) {
  {
    typedef optional<X> O;

    constexpr O o1;    // disengaged
    constexpr O o2;    // disengaged
    constexpr O o3{1}; // engaged
    constexpr O o4{2}; // engaged
    constexpr O o5{1}; // engaged

    static_assert(!(o1 < o1), "");
    static_assert(!(o1 < o2), "");
    static_assert((o1 < o3), "");
    static_assert((o1 < o4), "");
    static_assert((o1 < o5), "");

    static_assert(!(o2 < o1), "");
    static_assert(!(o2 < o2), "");
    static_assert((o2 < o3), "");
    static_assert((o2 < o4), "");
    static_assert((o2 < o5), "");

    static_assert(!(o3 < o1), "");
    static_assert(!(o3 < o2), "");
    static_assert(!(o3 < o3), "");
    static_assert((o3 < o4), "");
    static_assert(!(o3 < o5), "");

    static_assert(!(o4 < o1), "");
    static_assert(!(o4 < o2), "");
    static_assert(!(o4 < o3), "");
    static_assert(!(o4 < o4), "");
    static_assert(!(o4 < o5), "");

    static_assert(!(o5 < o1), "");
    static_assert(!(o5 < o2), "");
    static_assert(!(o5 < o3), "");
    static_assert((o5 < o4), "");
    static_assert(!(o5 < o5), "");
  }
  {
    using O1 = optional<int>;
    using O2 = optional<long>;
    constexpr O1 o1(42);
    static_assert(o1 < O2(101), "");
    static_assert(!(O2(101) < o1), "");
  }
  {
    using O1 = optional<int>;
    using O2 = optional<const int>;
    constexpr O1 o1(42);
    static_assert(o1 < O2(101), "");
    static_assert(!(O2(101) < o1), "");
  }

  return 0;
}