Is it possible to “store” a template parameter pack without expanding it?

Question

I was experimenting with C++0x variadic templates when I stumbled upon this issue:

template < typename ...Args >
struct identities
{
    typedef Args t         


        

Answer 1

This is a variation of GManNickG's neat partial specialization trick. No delegation, and you get more type safety by requiring the use of your variadic_typedef struct.

#include 

template
struct variadic_typedef {};

template
struct convert_in_tuple {
    //Leaving this empty will cause the compiler
    //to complain if you try to access a "type" member.
    //You may also be able to do something like:
    //static_assert(std::is_same<>::value, "blah")
    //if you know something about the types.
};

template
struct convert_in_tuple< variadic_typedef > {
    //use Args normally
    typedef std::tuple type;
};

typedef variadic_typedef myTypes;
typedef convert_in_tuple::type int_float_tuple; //compiles
//typedef convert_in_tuple::type int_float_tuple; //doesn't compile

int main() {}