How to use a noncopyable object as a slot with boost::signals2::signal

Question

I have an instance of a noncopyable object, that I want to use with a boost signal2. The connect method expects my functor to be copyable. Is there a way to work this around? How do I remove the comment in the code below?

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

struct Noncopyable
{
  Noncopyable() {};
  void operator()() { std::cerr << "hi Noncopyable" << std::endl; }
 private:
  Noncopyable(Noncopyable const&);
};

int main(void)
{
  Noncopyable no_copy;
  boost::signals2::signal<void ()> sig;
  //sig.connect(no_copy);
  sig();
}

Is there a way to pass a reference to no_copy object into connect method?

Answer 1

Use boost::ref (or std::ref) function to pass such an object by reference:

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

struct Noncopyable
{
  Noncopyable() {};
  void operator()() { std::cerr << "hi Noncopyable" << std::endl; }
 private:
  Noncopyable(Noncopyable const&);
};

int main(void)
{
  Noncopyable no_copy;
  boost::signals2::signal<void ()> sig;
  sig.connect(boost::ref(no_copy));
  sig();
}

Of course, ensure that no_copy object lives at least as long as it's connected to sig.