variadic template unpacking arguments to typename

Question

I want to unpack the parameter pack in func (see line A), but it doesnt work. How can I unpack inside func< > or modify Line A only?

#include <iostream>
using namespace std;

void func()
{
   cerr << "EMPTY" << endl;
}

template <class A, class ...B> void func()
{
   cerr << "A: "  << endl;
   func<B... >(); // line A
}


int main(void)
{
   func<int,int>();
   return 0;
}

An expected output :

A:
A:

edited: all of answers are very good. thanks alot

Answer 1

Sometimes it's easier to unpack everything at once, instead of recursively. If you simply want a parameter pack for_each, you can use a variant of the braced-init-list expansion trick (Live demo at Coliru):

template <class A>
void process_one_type() {
    cerr << typeid(A).name() << ' ';
}

template <class ...B> void func()
{
    int _[] = {0, (process_one_type<B>(), 0)...};
    (void)_;
    cerr << '\n';
}