learn and live

#include <tuple>
#include <iostream>
#include <string>
#include <stdexcept>

std::tuple<double, char, std::string> get_student(int id)
{
    // C++11构建tuple的写法
    if (id == 0) return std::make_tuple(3.8, 'A', "Lisa Simpson");

    // C++17提供了更方便的构建tuple的写法
    //if (id == 0) return { 3.8, 'A', "Lisa Simpson" };

    if (id == 1) return std::make_tuple(2.9, 'C', "Milhouse Van Houten");
    if (id == 2) return std::make_tuple(1.7, 'D', "Ralph Wiggum");
    throw std::invalid_argument("id");
}

int main()
{
    auto student0 = get_student(0);
    // 通过下标位置获取tuple中对应的元素
    std::cout << "ID: 0, "
              << "GPA: " << std::get<0>(student0) << ", "
              << "grade: " << std::get<1>(student0) << ", "
              << "name: " << std::get<2>(student0) << '\n';

    // 通过tie将tuple中的元素解构至多个变量中
    double gpa1;
    char grade1;
    std::string name1;
    std::tie(gpa1, grade1, name1) = get_student(1);
    std::cout << "ID: 1, "
              << "GPA: " << gpa1 << ", "
              << "grade: " << grade1 << ", "
              << "name: " << name1 << '\n';

    // C++17提供了更方便的解构写法
    //auto [ gpa2, grade2, name2 ] = get_student(2);
    //std::cout << "ID: 2, "
    //          << "GPA: " << gpa2 << ", "
    //          << "grade: " << grade2 << ", "
    //          << "name: " << name2 << '\n';
}

struct student {
  double gpa;
  char grade;
  std::string name;
};

student get_student(int id) {
  if (id == 0) {
    student s;
    s.gpa = 3.8;
    s.grade = 'A';
    s.name = "Lisa Simpson";
    return s;
  }
  // ...省略构建其余id的重复代码，只做简单演示
}

int main {
  auto student0 = get_student(0);

  std::cout << "ID: 0, "
            << "GPA: " << student0.gpa << ", "
            << "grade: " << student0.grade << ", "
            << "name: " << student0.name << '\n';
  // ...省略获取其余id的重复代码，只做简单演示
}

std::pair<double, std::pair<char, std::string> > get_student(int id) {
  if (id == 0) {
    return std::make_pair(3.8, std::make_pair('A', "Lisa Simpson"));
  }
  // ...省略构建其余id的重复代码，只做简单演示
}

int main() {
  auto student0 = get_student(0);
  std::cout << "ID: 0, "
            << "GPA: " << student0.first << ", "
            << "grade: " << student0.second.first << ", "
            << "name: " << student0.second.second << '\n';
  // ...省略获取其余id的重复代码，只做简单演示
  return 0;
}