比较两组类型是否相等 [英] Compare two sets of types for equality

问题描述

如何忽略两个参数包而忽略它们的内部顺序？

How can one check if two parameter packs are the same, ignoring their internal order?

到目前为止，我只有框架（使用 std :: tuple ），但没有功能。

So far I only have the frame (using std::tuple), but no functionality.

#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多次出现。

Every type is not allowed to occur more than once in a set.

推荐答案

如果元组中的类型是唯一的，则可以使用继承来回答第一个元组中的所有类型是否都作为基础。辅助结构。例如。 （C ++ 11方法）：

If types in tuples are unique you could make use of inheritance to answer if all types from the first tuple are involved as a base of the helper struct. E.g. (C++11 approach):

#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");
}

[实时演示]

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