#pragma once

namespace std
{

template<typename U, typename V> constexpr bool _is_same_helper = false;
template<typename T> constexpr bool _is_same_helper<T, T> = true;
template<typename U, typename V> concept same_as = _is_same_helper<U, V> && _is_same_helper<V, U>;

template<typename T> struct remove_reference { using type = T; };
template<typename T> struct remove_reference<T&> { using type = T; };
template<typename T> struct remove_reference<T&&> { using type = T; };
template<typename T> using remove_reference_t = remove_reference<T>::type;

template<typename T>
constexpr remove_reference_t<T>&& move(T&& r) noexcept
{
    return static_cast<remove_reference_t<T>&&>(r);
}

template<typename T>
constexpr T&& forward(remove_reference_t<T>& r) noexcept
{
    return static_cast<T&&>(r);
}

template<typename T>
constexpr T&& forward(remove_reference_t<T>&& r) noexcept // NOLINT
{
    return static_cast<T&&>(r);
}

template<typename T, typename U>
constexpr T exchange(T& obj, U&& new_value)
{
    T old_value = std::move(obj);
    obj = std::forward<U>(new_value);
    return old_value;
}

} // namespace std

static_assert(std::same_as<int, int>, "");
static_assert(!std::same_as<int, void>, "");

static_assert(std::same_as<std::remove_reference_t<int>, int>, "");
static_assert(std::same_as<std::remove_reference_t<int&>, int>, "");
static_assert(std::same_as<std::remove_reference_t<int&&>, int>, "");