Variadic template pack expansion

#include <iostream>

template <typename T>
void bar(T t) { std::cout << t << '\n'; }

template <typename... Args>
void foo2(Args&&... args)
{
  __attribute__((unused)) int dummy[] = { 0, ((void) bar(std::forward<Args>(args)),0)... };
}

int main()
{
  foo2();
  foo2 (1, 2, 3, "30");
}


One of the places where a pack expansion can occur is inside a braced-init-list. You can take advantage of this by putting the expansion inside the initializer list of a dummy array:

template<typename... Args>
static void foo2(Args &&... args)
{
    int dummy[] = { 0, ( (void) bar(std::forward<Args>(args)), 0) ... };
}

To explain the content of the initializer in more detail:

{ 0, ( (void) bar(std::forward<Args>(args)), 0) ... };
  |       |       |                        |     |
  |       |       |                        |     --- pack expand the whole thing 
  |       |       |                        |   
  |       |       --perfect forwarding     --- comma operator
  |       |
  |       -- cast to void to ensure that regardless of bar()'s return type
  |          the built-in comma operator is used rather than an overloaded one
  |
  ---ensure that the array has at least one element so that we don't try to make an
     illegal 0-length array when args is empty

C++17: Fold expressions

template<typename ...Args> auto sum(Args ...args) 
{ 
    return (args + ... + 0); 
}

// or even:

template<typename ...Args> auto sum2(Args ...args) 
{ 
    return (args + ...);
}