比较两组类型是否相等

Question

如何检查两个参数包是否相同,忽略它们的内部顺序？

到目前为止,我只有框架(使用std::tuple),但没有功能.

#include <tuple>
#include <type_traits>

template <typename, typename>
struct type_set_eq : std::false_type
{
};

template <typename ... Types1, typename ... Types2>
struct type_set_eq<std::tuple<Types1...>, std::tuple<Types2...>>
    : std::true_type
{
    // Should only be true_type if the sets of types are equal
};

int main() {
    using t1 = std::tuple<int, double>;
    using t2 = std::tuple<double, int>;
    using t3 = std::tuple<int, double, char>;

    static_assert(type_set_eq<t1, t1>::value, "err");
    static_assert(type_set_eq<t1, t2>::value, "err");
    static_assert(!type_set_eq<t1, t3>::value, "err");
}

每个类型不允许在一个集合中出现多次.

Answer 1

Boost.Hana解决方案:

constexpr auto t1 = hana::tuple_t<int, double>;
constexpr auto t2 = hana::tuple_t<double, int>;
constexpr auto t3 = hana::tuple_t<int, double, char>;

auto same = [](auto a, auto b)
{
    auto to_occurrences_map = [](auto t)
    {
        return hana::fold(t, hana::make_map(), [](auto m, auto x)
        { 
            if constexpr(!hana::contains(decltype(m){}, x)) 
            { 
                return hana::insert(m, hana::make_pair(x, 1)); 
            }
            else { return ++(m[x]); }
        });
    };

    return to_occurrences_map(a) == to_occurrences_map(b);
};

static_assert(same(t1, t1));
static_assert(same(t1, t2));
static_assert(!same(t1, t3));

直播wandbox示例

Answer 2

如果元组中的类型是唯一的,那么如果第一个元组中的所有类型都作为辅助结构的基础,则可以使用继承来回答.例如(C++ 11方法):

#include <tuple>
#include <type_traits>

template <class T>
struct tag { };

template <class... Ts>
struct type_set_eq_helper: tag<Ts>... { };

template <class, class, class = void>
struct type_set_eq: std::false_type { };

template <bool...>
struct bool_pack { };

template <bool... Bs>
using my_and = std::is_same<bool_pack<Bs..., true>, bool_pack<true, Bs...>>;

template <class... Ts1, class... Ts2>
struct type_set_eq<std::tuple<Ts1...>, std::tuple<Ts2...>, typename std::enable_if< (sizeof...(Ts1) == sizeof...(Ts2)) && my_and< std::is_base_of<tag<Ts2>, type_set_eq_helper<Ts1...>>::value...  >::value  >::type  >:
   std::true_type { };

int main() {
    using t1 = std::tuple<int, double>;
    using t2 = std::tuple<double, int>;
    using t3 = std::tuple<int, double, char>;

    static_assert(type_set_eq<t1, t1>::value, "err");
    static_assert(type_set_eq<t1, t2>::value, "err");
    static_assert(!type_set_eq<t1, t3>::value, "err");
}

[现场演示]