How can I store a boost::bind object as a class member?

Question

I\'m writing an application that uses boost::asio. Asio\'s async_receive (or async_read) is invariably shown using a boost::bind

Answer 1

The "standard" way of doing this is to make functor be a std::function.

If you really want to store the actual binder object, then look at compile error messages involving the binder to figure out the exact type, and try using those to determine the actual type of the binder object.

Answer 2

The return type of boost::bind is a boost::function. Here's a quick example using a very simple function:

double f(int i, double d) { 
    cout << "int = " << i << endl; 
    return d; 
} 

boost::function<double (int)> bound_func = boost::bind(f, _1, 1.234); 
int i = 99; 
cout << bound_func(i) << endl;

In your case the function has this type:

boost::function<void(const error_code, const size_t)> f;

Answer 3

Use boost::function:

class Whatever
{
public:
    Whatever()
    {
        functor = boost::bind(
            &chat_session::handle_read_header,
            shared_from_this(),
            boost::asio::placeholders::error,
            boost::asio::placeholders::bytes_transferred
        );
        boost::asio::async_read(
            socket_,
            boost::asio::buffer(
               read_msg_.data(),
               chat_message::header_length
            ),
            functor
        );
    }
private:
    boost::function<void(const error_code, const size_t)> functor;
};

... or something like that.

Answer 4

I guess you are looking for boost function.
You can assign the result of your bind expression to a boost::function object as long as the signature is correct.