CppPatterns/Functor/main.cpp

#include <iostream>
#include <numeric>
#include <vector>

class join_strings_functor {
private:
  std::string separator_ = " ";

public:
  join_strings_functor() = default;
  join_strings_functor(std::string_view separator) : separator_(separator) {}

  std::string operator()(const std::string &left,
                         const std::string &right) const {
    return left + separator_ + right;
  }
};

int main(int argc, char *argv[]) {

  std::cout << "Functor" << std::endl;

  std::vector<std::string> names = {"Albert", "Bernd", "Cora",
                                    "Dave",   "Emil",  "Frank"};

  auto space_joined_string =
      std::accumulate(std::next(names.begin()), names.end(), names.front(),
                      join_strings_functor());

  std::cout << "Space-joined string: " << space_joined_string << std::endl;

  auto comma_joined_string =
      std::accumulate(std::next(names.begin()), names.end(), names.front(),
                      join_strings_functor(", "));

  std::cout << "Comma-joined string: " << comma_joined_string << std::endl;

  return EXIT_SUCCESS;
}