C++ 模板 lambda 包装器

Question

谁能知道如何进行编译？

我正在尝试将 lambda 包装在另一个执行某些操作的函数中（此处打印“你知道什么”）+ 调用 lambda。

最好是自动扣除模板参数。

#include <iostream>
#include <functional>
#include <utility>

void youKnowWhat(const std::function<void()>&& fun)
{
    std::cout << "You know what ?" << std::endl;
    fun();
}

template <typename... Args>
auto youKnowWhatSomething(const std::function<void(Args...)>&& fun)
{
    return [fun{std::move(fun)}](Args... args)
        {
            youKnowWhat(std::bind(fun, std::forward<Args>(args)...));
        };
}

int main()
{
    const auto imHavingSomething([](const std::string& s){
        std::cout << "Im having " << s << std::endl;
    });

    const auto youKnowWhatImHavingSomething(youKnowWhatSomething(std::move(imHavingSomething)));
    youKnowWhatImHavingSomething("fun with templates");
    youKnowWhatImHavingSomething("headaches");
}

Answer 1

这对你有用吗？我（基本上）从 const ... && 中删除了 const，并向函数 youKnowWhatSomething 添加了一个模板参数。 lambda 不再在 main.

中声明为 const

#include <iostream>
#include <functional>
#include <utility>

void youKnowWhat(const std::function<void()>& fun)
{
    std::cout << "You know what ?" << std::endl;
    fun();
}

template<typename function_t, typename... Args>
auto youKnowWhatSomething(function_t&& fun)
{
    return [fun{std::move(fun)}](Args... args)
        {
            youKnowWhat(std::bind(fun, std::forward<Args>(args)...));
        };
}

int main() {
    auto imHavingSomething = [](std::string s) {
        std::cout << "Im having " << s << std::endl;
    };

    const auto youKnowWhatImHavingSomething =
        youKnowWhatSomething<decltype(imHavingSomething), std::string>
        (std::move(imHavingSomething));

    youKnowWhatImHavingSomething("fun with templates");
    youKnowWhatImHavingSomething("headaches");
}

Answer 2

怎么样

#include <iostream>
#include <functional>
#include <utility>

template <typename F>
void youKnowWhat(F&& fun)
{
    std::cout << "You know what ?" << std::endl;
    fun();
}

template <typename F>
auto youKnowWhatSomething(F&& fun)
{
    return [fun{std::move(fun)}](auto&&... args) -> decltype(fun(std::forward<decltype(args)>(args)...), void())
        {
            youKnowWhat([&](){fun(std::forward<decltype(args)>(args)...); });
        };
}

int main()
{
    const auto imHavingSomething([](std::string s){
        std::cout << "Im having " << s << std::endl;
    });

    const auto youKnowWhatImHavingSomething(youKnowWhatSomething(imHavingSomething));
    youKnowWhatImHavingSomething("fun with templates");
    youKnowWhatImHavingSomething("headaches");
}

Demo

C++ 模板 lambda 包装器

C++ template lambda wrapper

c++

lambda

templates