Binding class member functions for boost::signals2

Question

I have used std::bind to create a lambda involving a class member function but boost::signals2 won't accept it.

I have a class Cut which I would like to inform when there is a new Event to look at by calling void Cut::newEvent(Event& e).

I created a lambda binding to an instance of Cut and this works as expected when I pass it an Event. (The code compiles and the output is "Registered new event".)

However when I try to connect this lambda to an instance of boost::signals2::signal<void(Event&)> it complains with the message:

error: 'f' cannot be used as a function

which is odd because I can use it as a function in main(). ( I get the same result if I use std::function<void(Event&)> instead of auto.

Is it possible to make this work? Why doesn't it currently work?

This is relevant code:

#include <iostream>
#include <boost/signals2.hpp>

//Dummy event class
struct Event
{ int val; };

typedef boost::signals2::signal<void (Event&) >
EventBroadcaster;

//Class I want to notified of new events
class Cut
{
    public:
        void newEvent( Event& e)
        {
            std::cout << "Registered new event" << std::endl;
            fResult = true;
        }

        bool check() const
        { return fResult; }

    private:
        bool fResult;
};

int main()
{

    Cut c{};

    //Lambda to call newEvent on c
    auto f =
        std::bind( &Cut::newEvent, &c,
                std::placeholders::_1) ;

    Event e{};
    f(e); //works

    EventBroadcaster eb;
    eb.connect(&f); //doesn't work
}

Answer 1

You should use

eb.connect(f);

since f is callable function object, but &f is not callable.