#include <concepts>
#include <iostream>

template <std::integral T>  // 約束 T 必須是整數(shù)類(lèi)型
T add(T a, T b) {
    return a + b;
}

int main() {
    std::cout << add(3, 4) << "\n"; // OK
    // std::cout << add(3.5, 4.2); // 編譯錯(cuò)誤：double 不是整數(shù)
}

#include <ranges>
#include <vector>
#include <iostream>

int main() {
    std::vector<int> v = {1, 2, 3, 4, 5};
    for (int x : v | std::views::filter([](int n) { return n % 2 == 0; })) {
        std::cout << x << " ";  // 輸出: 2 4
    }
}

#include <coroutine>
#include <iostream>

struct Task {
    struct promise_type {
        Task get_return_object() { return {}; }
        std::suspend_never initial_suspend() { return {}; }
        std::suspend_never final_suspend() noexcept { return {}; }
        void return_void() {}
        void unhandled_exception() {}
    };
};

Task example() {
    std::cout << "Hello, ";
    co_await std::suspend_always{};
    std::cout << "World!\n";
}

int main() {
    example();  // 輸出: Hello,
}

#include <span>
#include <iostream>

void print(std::span<int> s) {
    for (int n : s) std::cout << n << " ";
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    print(arr);  // 自動(dòng)推導(dǎo)為 span
}

#include <iostream>
#include <compare>

struct Point {
    int x, y;
    auto operator<=>(const Point&) const = default;  // 自動(dòng)生成所有比較運(yùn)算符
};

int main() {
    Point p1{1, 2}, p2{2, 3};
    std::cout << (p1 < p2) << "\n";  // 輸出: 1 (true)
}

#include <vector>

constexpr int sum(const std::vector<int>& v) {
    int total = 0;
    for (int n : v) total += n;
    return total;
}

int main() {
    constexpr std::vector<int> v = {1, 2, 3, 4, 5};
    static_assert(sum(v) == 15);
}

// mymodule.cpp
export module mymodule;
export int add(int a, int b) { return a + b; }

// main.cpp
import mymodule;
#include <iostream>

int main() {
    std::cout << add(3, 4) << "\n";  // 輸出: 7
}

#include <thread>
#include <iostream>

int main() {
    std::jthread t([] { std::cout << "Running in thread\n"; });
}  // `t` 自動(dòng) `join()`，無(wú)需手動(dòng)管理

#include <bit>
#include <iostream>

int main() {
    float f = 3.14f;
    int i = std::bit_cast<int>(f);
    std::cout << i << "\n";  // 按位轉(zhuǎn)換，無(wú)額外開(kāi)銷(xiāo)
}

#include <format>
#include <iostream>

int main() {
    std::cout << std::format("Hello, {}!", "world") << "\n";  // 輸出: Hello, world!
}

#include <ranges>
#include <vector>
#include <iostream>

int main() {
    std::vector<int> a = {1, 2, 3};
    std::vector<std::string> b = {"one", "two", "three"};

    for (auto [x, y] : std::views::zip(a, b)) {
        std::cout << x << " -> " << y << "\n";
    }
}

#include <iostream>
#include <thread>
#include <stop_token>

void task(std::stop_token st) {
    while (!st.stop_requested()) {
        std::cout << "Working...\n";
        std::this_thread::sleep_for(std::chrono::milliseconds(500));
    }
}

int main() {
    std::jthread t(task);
    std::this_thread::sleep_for(std::chrono::seconds(2));
    t.request_stop();  // 取消線程
}