#include <functional>
#include <iostream>
 
void apply(std::function<void()> f, int) {
  f();
}
 
template <typename Head, typename ...Tail>
void apply(std::function<void(Head, Tail...)> f, int i=0) {
  auto g = [=](Tail&& ...args){
    f(i, std::forward<Tail>(args)...);
  };
 
  apply(std::function<void(Tail...)>{g}, ++i);
}
 
void foo(int a, int b, int c, int d) {
  std::cout << a << b << c << d << "\n";
}
 
int main() {
  auto f = std::function<void(int,int,int,int)>(foo);
  apply(f);
}
 

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