initializer_list.cc

#include <boost/utility/string_ref.hpp>
#include <utility>
#include <iostream>

std::size_t all_length(std::initializer_list<boost::string_ref> ss) {
  std::size_t n = 0;
  for (auto const& s : ss) {
    n += s.size();
  }
  return n;
}

template<class... Args,
  // SFINAE
  class = decltype(
      std::initializer_list<boost::string_ref>{std::declval<Args>()...})
>
std::size_t all_length(Args&&... args) {
  return ::all_length({std::forward<Args>(args)...});
}

int main() {
  std::string s = "hoge";
  std::cout << all_length({}) << std::endl;
  std::cout << all_length({"hoge"}) << std::endl;
  std::cout << all_length() << std::endl;
  std::cout << all_length("hoge") << std::endl;
  std::cout << all_length("foo", s, "gonyogonyo") << std::endl;
}