Print value category and constness of a universal reference for all the different argument options

test_uref_types.cpp

#include <iostream>
#include <type_traits>
#include <utility>


namespace {

struct Func
{
    Func() = default;

    Func(const Func&) = delete;
    Func& operator= (const Func&) = delete;
    Func(Func&&) = delete;
    Func& operator= (Func&&) = delete;

    const char *operator() () &  { return "L_value"; }
    const char *operator() () && { return "R_value"; }
    const char *operator() () const &  { return "const L_value"; }
    const char *operator() () const && { return "const R_value"; }
};


inline const char *category_name(bool lvalue_ref, bool rvalue_ref)
{
    if (lvalue_ref)
        return "L_value reference";
    if (rvalue_ref)
        return "R_value reference";
    return "value";
}

#define TYPE_INFO(type__)  \
    (std::is_lvalue_reference<type__>::value ? (std::is_const<typename std::remove_reference<type__>::type>::value ? "const L_value ref" : "L_value ref")  \
     : std::is_rvalue_reference<type__>::value ? (std::is_const<typename std::remove_reference<type__>::type>::value ? "const R_value ref" : "R_value ref")  \
         : std::is_const<type__>::value ? "const value" : "value")


template<class F>
void func(F && f)
{
    std::cout
        << "forward<F>:           " << (std::forward<F>(f)()) << "\n"
        << "forward<decltype(f)>: " << (std::forward<decltype(f)>(f)()) << "\n"
        << "forward<F&&>:         " << (std::forward<F&&>(f)()) << "\n"
        << "std::move:            " << (std::move(f)()) << "\n"
        << "nothing:              " << (f()) << "\n"
        ;
    std::cout
        << "F:           " << TYPE_INFO(F) << "\n"
        << "decltype(f): " << TYPE_INFO(decltype(f)) << "\n"
        << "F&&:         " << TYPE_INFO(F&&) << "\n"
        ;
}
}

int main()
{
    Func f1{};

    std::cout << "L_value:\n";
    func(f1);

    std::cout << "\nR_value:\n";
    func(std::move(f1));

    std::cout << "\nR_value:\n";
    func(Func{});

    const Func f2{};

    std::cout << "\nconst L_value:\n";
    func(f2);

    std::cout << "\nconst R_value:\n";
    func(std::move(f2));

    return 0;
}