llvm-project/libcxx/test/std/utilities/function.objects/refwrap/weak_result.pass.cpp

//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

// <functional>

// reference_wrapper

// has weak result type

#include <functional>
#include <type_traits>

template <class Arg, class Result>
struct my_unary_function
{ // std::unary_function was removed in C++17
    typedef Arg argument_type;
    typedef Result result_type;
};

template <class Arg1, class Arg2, class Result>
struct my_binary_function
{ // std::binary_function was removed in C++17
    typedef Arg1 first_argument_type;
    typedef Arg2 second_argument_type;
    typedef Result result_type;
};

class functor1
    : public my_unary_function<int, char>
{
};

class functor2
    : public my_binary_function<char, int, double>
{
};

class functor3
    : public my_unary_function<char, int>,
      public my_binary_function<char, int, double>
{
public:
    typedef float result_type;
};

class functor4
    : public my_unary_function<char, int>,
      public my_binary_function<char, int, double>
{
public:
};

class C {};

template <class T>
struct has_result_type
{
private:
    struct two {char _; char __;};
    template <class U> static two test(...);
    template <class U> static char test(typename U::result_type* = 0);
public:
    static const bool value = sizeof(test<T>(0)) == 1;
};

int main()
{
    static_assert((std::is_same<std::reference_wrapper<functor1>::result_type,
                                char>::value), "");
    static_assert((std::is_same<std::reference_wrapper<functor2>::result_type,
                                double>::value), "");
    static_assert((std::is_same<std::reference_wrapper<functor3>::result_type,
                                float>::value), "");
    static_assert((std::is_same<std::reference_wrapper<void()>::result_type,
                                void>::value), "");
    static_assert((std::is_same<std::reference_wrapper<int*(double*)>::result_type,
                                int*>::value), "");
    static_assert((std::is_same<std::reference_wrapper<void(*)()>::result_type,
                                void>::value), "");
    static_assert((std::is_same<std::reference_wrapper<int*(*)(double*)>::result_type,
                                int*>::value), "");
    static_assert((std::is_same<std::reference_wrapper<int*(C::*)(double*)>::result_type,
                                int*>::value), "");
    static_assert((std::is_same<std::reference_wrapper<int (C::*)(double*) const volatile>::result_type,
                                int>::value), "");
    static_assert((std::is_same<std::reference_wrapper<C()>::result_type,
                                C>::value), "");
    static_assert(has_result_type<std::reference_wrapper<functor3> >::value, "");
    static_assert(!has_result_type<std::reference_wrapper<functor4> >::value, "");
    static_assert(!has_result_type<std::reference_wrapper<C> >::value, "");
}