源码展示:
#include <iostream>
using namespace std;
template <typename ... Args> struct typelist;
typedef typelist <int ，short ，double ，long ，float> defaultPolicys;
template <typename A， typename B> struct concat;
template <typename... A， typename... B>
struct concat<typelist<A...>， typelist<B...> >
{
typedef typelist<A...， B...> type;
};
template<typename T， typename... TList>
struct concat<typelist<TList...>， T >
{
typedef typelist<TList...， T> type;
};
template<typename T， typename... TList>
struct concat< T， typelist<TList...> >
{
typedef typelist<T， TList...>  type;
};
template <typename T ，int I， typename K= defaultPolicys> struct replace;
template <typename T， int I， typename H，typename ...Tail> struct replace<T，I，typelist<H，Tail...>>
{
typedef typename concat<H， typename replace<T， I-1， typelist<Tail...>>::type>::type type;
};
template <typename T，typename H，typename... Tail> struct replace<T，0，typelist<H，Tail...>>
{
typedef typelist<T，Tail...> type;
};
template <typename T ，int I> struct Custom
{
const static int index = I;
typedef T newType;
};
template <typename ...> struct CEO;
template <> struct CEO<>
{
typedef defaultPolicys myPolicys;
};
template <typename T> struct CEO<T>
{
typedef typename replace<typename T::newType，T::index>::type myPolicys;
};
//template <typename T，typename U> struct CEO<T，U>{ typedef typename replace<typename U::newType，U::index，typename CEO<T>::myPolicys>::type myPolicy;};
template <typename T，typename ... Tail> struct CEO<T，Tail...>
{
typedef typename replace<typename T::newType，T::index，typename CEO<Tail...>::myPolicys>::type myPolicys;
};
int main()
{
typedef typelist <int ，short ，double ，long ，float> five;
typedef typelist <int ，short ，string， char ，string> fives;
if(is_same<typename CEO<>::myPolicys，five>::value)cout<<"..."<<endl;
if(is_same< CEO< Custom<string，2>，Custom<char，3>，Custom<string，4> > ::myPolicys，fives>::value)cout<<"..."<<endl;
return 0;
}