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//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
// <functional>
//
// UNSUPPORTED: c++03, c++11, c++14, c++17
//
// common_reference specializations for reference_wrapper
#include <concepts>
#include <functional>
#include <type_traits>
template <class T>
concept HasType = requires { typename T::type; };
template <class Result, class T1, class T2>
concept check_XY = std::same_as<Result, std::common_reference_t<T1, T2>>;
template <class Result, class T1, class T2>
concept check_YX = std::same_as<Result, std::common_reference_t<T2, T1>>;
template <class Result, class T1, class T2>
concept check = check_XY<Result, T1, T2> && check_YX<Result, T1, T2>;
template <class T1, class T2>
concept check_none_XY = !HasType<std::common_reference<T1, T2>>;
template <class T1, class T2>
concept check_none_YX = !HasType<std::common_reference<T2, T1>>;
template <class T1, class T2>
concept check_none = check_none_XY<T1, T2> && check_none_YX<T1, T2>;
// https://eel.is/c++draft/meta.trans#other-2.4
template <class X, class Y>
using CondRes = decltype(false ? std::declval<X (&)()>()() : std::declval<Y (&)()>()());
template <class X, class Y>
struct Ternary {};
template <class X, class Y>
requires requires() { typename CondRes<X, Y>; }
struct Ternary<X, Y> {
using type = CondRes<X, Y>;
};
template <class X, class Y>
using Ternary_t = typename Ternary<X, Y>::type;
template <class T>
using Ref = std::reference_wrapper<T>;
using std::common_reference_t;
using std::same_as;
// clang-format off
static_assert(check<int & , Ref<int >, int & >);
static_assert(check<int const&, Ref<int >, int const& >);
static_assert(check<int const&, Ref<int const>, int & >);
static_assert(check<int const&, Ref<int const>, int const& >);
static_assert(check<int&, Ref<int> const&, int& >);
static_assert(check<const volatile int&, Ref<const volatile int>, const volatile int&>);
// derived-base and implicit convertibles
struct B {};
struct D : B {};
struct C {
operator B&() const;
};
static_assert(check<B& , Ref<B>, D & >);
static_assert(check<B const&, Ref<B>, D const&>);
static_assert(check<B const&, Ref<B const>, D const&>);
static_assert(check<B& , Ref<D>, B & >);
static_assert(check<B const&, Ref<D>, B const&>);
static_assert(check<B const&, Ref<D const>, B const&>);
static_assert(std::same_as<B&, CondRes<Ref<D>, B&>>);
static_assert(std::same_as<B const&, CondRes<Ref<D>, B const &>>);
static_assert(std::same_as<B const&, CondRes<Ref<D const>, B const&>>);
static_assert( check<B& , Ref<B> , C& >);
static_assert( check<B& , Ref<B> , C >);
static_assert( check<B const& , Ref<B const>, C >);
static_assert(!check<B& , Ref<C> , B& >); // Ref<C> cannot be converted to B&
static_assert( check<B& , Ref<B> , C const&>); // was const B& before P2655R3
using Ri = Ref<int>;
using RRi = Ref<Ref<int>>;
using RRRi = Ref<Ref<Ref<int>>>;
static_assert(check<Ri&, Ri&, RRi>);
static_assert(check<RRi&, RRi&, RRRi>);
static_assert(check<Ri, Ri, RRi>);
static_assert(check<RRi, RRi, RRRi>);
static_assert(check_none<int&, RRi>);
static_assert(check_none<int, RRi>);
static_assert(check_none<int&, RRRi>);
static_assert(check_none<int, RRRi>);
static_assert(check_none<Ri&, RRRi>);
static_assert(check_none<Ri, RRRi>);
template <typename T>
struct Test {
// Check that reference_wrapper<T> behaves the same as T& in common_reference.
using R1 = common_reference_t<T&, T&>;
using R2 = common_reference_t<T&, T const&>;
using R3 = common_reference_t<T&, T&&>;
using R4 = common_reference_t<T&, T const&&>;
using R5 = common_reference_t<T&, T>;
static_assert(same_as<R1, common_reference_t<Ref<T>, T&>>);
static_assert(same_as<R2, common_reference_t<Ref<T>, T const&>>);
static_assert(same_as<R3, common_reference_t<Ref<T>, T&&>>);
static_assert(same_as<R4, common_reference_t<Ref<T>, T const&&>>);
static_assert(same_as<R5, common_reference_t<Ref<T>, T>>);
// commute:
static_assert(same_as<R1, common_reference_t<T&, Ref<T>>>);
static_assert(same_as<R2, common_reference_t<T const&, Ref<T>>>);
static_assert(same_as<R3, common_reference_t<T&&, Ref<T>>>);
static_assert(same_as<R4, common_reference_t<T const&&, Ref<T>>>);
static_assert(same_as<R5, common_reference_t<T, Ref<T>>>);
// reference qualification of reference_wrapper is irrelevant
static_assert(same_as<R1, common_reference_t<Ref<T>&, T&>>);
static_assert(same_as<R1, common_reference_t<Ref<T> , T&>>);
static_assert(same_as<R1, common_reference_t<Ref<T> const&, T&>>);
static_assert(same_as<R1, common_reference_t<Ref<T>&&, T&>>);
static_assert(same_as<R1, common_reference_t<Ref<T> const&&, T&>>);
};
// clang-format on
// Instantiate above checks:
template struct Test<int>;
template struct Test<std::reference_wrapper<int>>;
// reference_wrapper as both args is unaffected.
// subject to simple first rule of
static_assert(check<Ref<int>&, Ref<int>&, Ref<int>&>);
// double wrap is unaffected.
static_assert(check<Ref<int>&, Ref<Ref<int>>, Ref<int>&>);
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