C++多参模板

多参模板的介绍

class Set {
public:
Set() {}
    Set(int a, bool b, std::string c) : a(a), b(b), c(c) {}

    void print() {
        std::cout << "abc->" << a << b << c << std::endl;
    }

private:
    int a;
    bool b;
    std::string c;
};

// 1. 多参的模板声明;
template<typename ...Args>

// 2. 多参的函数声明
void test(Args...params) {

    // 3-1. 多参的调用
    Set set(params...);
    set.print();
    
    // 3-2. 多参结合std::forward调用
    Set set1(std::forward<Args>(params)...);
    set1.print();
}

多参模板的实例

template <typename Task, typename... Args>
auto Executor::pushTo(bool front, Task task, Args&&... args) -> std::future<decltype(task(args...))> {
    // 去掉参数
    auto boundTask = 
        std::bind(std::forward<Task>(task), std::forward<Args>(args)...);
    using PackagedTaskType = std::packaged_task<decltype(boundTask())()>;
    // std::packaged_task指针，原型是std::packaged_task<decltype(boundTask())()> p(boundTask)
    auto packaged_task = std::make_shared<PackagedTaskType>(boundTask);

    // std::promise指针，原型是std::promise<decltypetask(args...))>> p;
    auto cleanupPromise = std::make_shared<std::promise<decltype(task(args...))>>();
    auto cleanupFuture = cleanupPromise->get_future();

    // 指针可以直接值传入
    auto translated_task = [packaged_task, cleanupPromise]() mutable {
        // Execute the task.
        packaged_task->operator()();
        // Note the future for the task's result.
        auto taskFuture = packaged_task->get_future();
        // Clean up the task.
        packaged_task.reset();
        // Forward the task's result to our cleanup promise/future.
        forwardPromise(cleanupPromise, &taskFuture);
    };

    // 释放packaged task的本地指针，现在唯一的引用在lambda中
    packaged_task.reset();
}