#include <utility>
std::pair<T1, T2> p;

#include <utility>
auto p = std::make_pair(x, y);

#include <utility>
std::swap(a, b);

#include <iostream>
#include <utility>

int main() {
    // 使用 make_pair 创建 pair 对象
    auto p = std::make_pair(10, 20);

    // 输出 pair 对象的元素
    std::cout << "First element: " << p.first << std::endl;
    std::cout << "Second element: " << p.second << std::endl;

    return 0;

}

First element: 10
Second element: 20

#include <iostream>
#include <utility>

int main() {
    int a = 5;
    int b = 10;

    std::cout << "Before swap: a = " << a << ", b = " << b << std::endl;

    // 使用 swap 函数交换 a 和 b 的值
    std::swap(a, b);

    std::cout << "After swap: a = " << a << ", b = " << b << std::endl;

    return 0;
}

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

#include <iostream>
#include <utility>
#include <vector>

int main() {
    std::vector<int> v1 = {1, 2, 3, 4, 5};
    std::vector<int> v2 = std::move(v1);

    std::cout << "v1 size: " << v1.size() << std::endl; // v1 现在为空
    std::cout << "v2 size: " << v2.size() << std::endl; // v2 拥有 v1 的元素

    return 0;
}

#include <iostream>
#include <utility>

void process(int& i) {

    std::cout << "Lvalue reference to " << i << std::endl;
}

void process(int&& i) {
    std::cout << "Rvalue reference to " << i << std::endl;
}

template <typename T>
void forward_example(T&& t) {
    process(std::forward<T>(t));
}

int main() {
    int x = 10;
    forward_example(x);           // Lvalue reference
    forward_example(20);          // Rvalue reference
    forward_example(std::move(x));// Rvalue reference

    return 0;

}

#include <iostream>
#include <utility>
#include <type_traits>

struct MyClass {
    MyClass(int, double) {}
};

template <typename T>
void test() {
    // 获取 T 的构造函数返回的类型，而不实际调用它
    using R = decltype(std::declval<T>()(1, 1.0));
    std::cout << std::is_same<R, MyClass>::value << std::endl;
}

int main() {
    test<MyClass>(); // 输出 1 (true)

    return 0;
}