Call member function for each element of std::tuple

Question

I've been searching the most simple and elegant solution and found this:

#include <iostream>
#include <utility>
#include <tuple>


struct A{
  void hi(){
    std::cout << "HI\n";
  }
};

template<typename Tuple, std::size_t... Is>
void unpack(Tuple& tpl, std::index_sequence<Is...>){
  ((std::get<Is>(tpl).hi()),...);
}

int main(){

  std::tuple<A,A,A,A,A,A> tpl { A(), A(), A(), A(), A(), A() };

  unpack(tpl, std::make_index_sequence<6>{});

  return 0;
}

However, i do not completely understand this line:

((std::get<Is>(tpl).hi()),...);

I understand what it does, but what is that kind of syntax?

Is it somewhere in standard?

https://eli.thegreenplace.net/2014/variadic-templates-in-c/ – Barmar Mar 30 '18 at 13:08 — Barmar, Mar 30 '18 at 13:08

score 0 · Accepted Answer · answered Mar 30 '18 at 13:09

0

This is a fold expression that does

(std::get<Is>(tpl).hi())

for every Is that is packed inside.

answered Mar 30 '18 at 13:09

Poeta Kodu

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Call member function for each element of std::tuple

1 Answers1