使用成员指针和闭包任意连接调用链

member_pointer.cpp

template <typename C, typename... P>
void connect(std::function<void()> &trigger, C *instance,
             void (C::*member_ptr)(P...), P... params) {
    trigger = [=]() {
        trigger();
        (instance->*member_ptr)(params...);
    };
}

struct A {
    void foo() { std::cout << "foooo" << std::endl; }
};

struct B {
    void bar(int n) { std::cout << "baaaar" << n << std::endl; }
};

void signal1() { std::cout << "signal with side effect" << std::endl; }

void signal2() {}

int main() {
    A a;
    B b;
    std::map<std::string, std::function<void()>> dispatch_map = {
        {"sig1", signal1}, {"sig2", signal2}};
    std::string input;
    do {
        std::getline(std::cin,input);
        if (input == "connect1a") {
            connect(dispatch_map["sig1"], &a, &A::foo);
        } else if (input == "connect2a") {
            connect(dispatch_map["sig2"], &a, &A::foo);
        } else if (input == "connect1b") {
            connect(dispatch_map["sig1"], &b, &B::bar, 1);
        } else if (input == "connect2b") {
            connect(dispatch_map["sig2"], &b, &B::bar, 2);
        } else if (input == "disconnect1") {
            dispatch_map["sig1"] = signal1;
        } else if (input == "disconnect2") {
            dispatch_map["sig2"] = signal2;
        }
        if (dispatch_map.find(input) != dispatch_map.end()) {
            dispatch_map[input]();
        }
    } while (!input.empty());
}