boost::signal2でshared_ptrを用いたトラッキングの方法

gistfile1.cpp

#include <iostream>

void hello()
{
    std::cout << "Hello ";
}

struct World
{
    void operator()()
    {
        std::cout << "World";
    }
};

struct CoutChar
{
    CoutChar(char c)
        : letter(c)
    {}

    void print()
    {
        std::cout << letter;
    }

    char letter;
};

#include <boost/signals2.hpp>

int main()
{
    World world;
    CoutChar c('!');
    using boost::signals2::signal;
    signal<void()> s;

    s.connect(&hello);
    s.connect(world);
    s.connect(std::bind(&CoutChar::print, c));
    s();
    std::cout << std::endl;

    s.disconnect_all_slots();
    s.connect(1, world);
    s.connect(0, &hello);
    s.connect(2, std::bind(&CoutChar::print, c));
    s();
    std::cout << std::endl;

    s.disconnect_all_slots();
    s.connect(1, world);
    s.connect(0, &hello);
    {
        std::shared_ptr<CoutChar> c(new CoutChar('!'));
        s.connect(2, signal<void()>::slot_type(&CoutChar::print, c.get()).track_foreign(c));
        std::cout << s.num_slots();
        std::cout << std::endl;
    }
    s();
    std::cout << std::endl;
    std::cout << s.num_slots();
    std::cout << std::endl;
}