如何检查两个参数包是否相同,忽略其内部顺序？
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");
}
每种类型不允许在一组中发生多次.
解决方法
如果元组中的类型是唯一的,则可以利用继承来回答,如果所有来自第一个元组的类型都作为辅助结构体的基础.例如. (C11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,"err");
}
[Live demo]