tie4.cpp

#include <tuple>
#include <string>
#include <iostream>
#include <iomanip>

class Person {
  std::string first_name_;
  std::string last_name_;
  int age_;
public:
  Person() = default;
  Person(const Person&) = default;
  Person(Person&&) = default;
  Person(std::string a, std::string b, int c) : first_name_{a}, last_name_{b}, age_{c} {}
  
  std::string first_name() const { return first_name_; }
  std::string last_name() const { return last_name_; }
  int age() const { return age_; }
};

bool operator<(const Person& x, const Person& y)
{
  // OK！forward_as_tupleがいいかんじに束縛してくれる！
  return std::forward_as_tuple(x.last_name(), x.first_name(), x.age()) < std::forward_as_tuple(y.last_name(), y.first_name(), y.age());
}

int main(){
    Person a = { "Y", "W", 21 };
    Person b = { "G", "W", 21 };
    std::cout << std::boolalpha << (a < b);
}