c++ - 自动从成员函数签名中推导 lambda 参数

Question

通常，我使用 lambda 函数来设置对第三方库的成员函数的回调。例如:

setCallback([this](auto&& ...x) { handleCallback(std::forward<decltype(x)>(x)...); });

现在我有一个带有重载函数的库来设置回调，使得这一行不明确:

#include <functional>
#include <iostream>

class Library
{
public:
    typedef std::function<void (int)> IntFunction;
    typedef std::function<void (int, int)> IntIntFunction;

    void setCallback(IntFunction f) { f_int_ = f; }
    void setCallback(IntIntFunction f) { f_int_int_ = f; }

    void callCallback(int a, int b) {
        if (f_int_) f_int_(a);
        if (f_int_int_) f_int_int_(a, b);
    }

private:
    IntFunction f_int_;
    IntIntFunction f_int_int_;
};

class MyClass
{
public:
    MyClass() {
        //lib.setCallback([this](auto&& ...x) { handleCallback(std::forward<decltype(x)>(x)...); });
        lib.setCallback([this](int a, int b) { handleCallback(a, b); });
    }

    void handleCallback(int a, int b) {
        std::cout << "handleCallback: " << a << ", " << b << std::endl;
    }

    Library lib;
};

int main()
{
    MyClass myclass;
    myclass.lib.callCallback(2, 3);
    return 0;
}

有没有办法自动从 handleCallback 函数中推导出正确的参数，以避免 lambda 中出现重复的函数参数？

Answer 1

您可以为此创建函数:

class MyClass
{
    template <typename Ret, typename ...Args>
    void setCallback(Ret (MyClass::*member)(Args...) /*const*/) {
        lib.setCallback([=](Args...args)
            {
                (this->*member)(std::forward<decltype(args)>(args)...);
            });
    }

public:
    MyClass() { setCallback(&MyClass::handleCallback); }

    void handleCallback(int a, int b) {
        std::cout << "handleCallback: " << a << ", " << b << std::endl;
    }

    Library lib;
};

Demo