一部纪录片，四十年 C++：从贝尔实验室的"带类的 C"到全球增长最快的主流语言

// evolution.cpp — 同一个任务，三种年代的写法
// 编译: g++ -std=c++20 -O2 evolution.cpp -o evolution

#include <iostream>
#include <vector>
#include <algorithm>
#include <ranges>
#include <string>

struct Person {
    std::string name;
    int age;
};

// ── 1998年风格：手写循环 + 谓词函数对象 ──
void print_adults_c98(const std::vector<Person>& people) {
    struct IsAdult {
        bool operator()(const Person& p) const { return p.age >= 18; }
    };
    struct GetName {
        std::string operator()(const Person& p) const { return p.name; }
    };

    std::vector<Person> adults;
    std::copy_if(people.begin(), people.end(), std::back_inserter(adults), IsAdult());

    std::vector<std::string> names;
    std::transform(adults.begin(), adults.end(), std::back_inserter(names), GetName());

    for (std::vector<std::string>::const_iterator it = names.begin();
         it != names.end(); ++it) {
        std::cout << *it << "\n";
    }
}

// ── 2011年风格：lambda + auto + 范围for ──
void print_adults_c11(const std::vector<Person>& people) {
    std::vector<std::string> names;
    std::for_each(people.begin(), people.end(), [&](const Person& p) {
        if (p.age >= 18) names.push_back(p.name);
    });
    for (const auto& name : names) {
        std::cout << name << "\n";
    }
}

// ── 2020年风格：Ranges + 管道组合 ──
void print_adults_c20(const std::vector<Person>& people) {
    for (const auto& name : people
             | std::views::filter([](const Person& p) { return p.age >= 18; })
             | std::views::transform([](const Person& p) { return p.name; })) {
        std::cout << name << "\n";
    }
}

int main() {
    std::vector<Person> team = {
        {"Alice", 30}, {"Bob", 16}, {"Carol", 22}, {"Dave", 14}, {"Eve", 45}
    };

    std::cout << "=== C++98 style ===\n";  print_adults_c98(team);
    std::cout << "=== C++11 style ===\n";  print_adults_c11(team);
    std::cout << "=== C++20 style ===\n";  print_adults_c20(team);
}