Using Bind with Signals (version 2)

30 May 2003

      Similar to my last post, this is a slightly different implementation
where the handler has a signal of its own.  Now I can't seem to bind to
the handler functor, getting a compiler message like:

/usr/include/boost/bind.hpp:60: error: `bool (handler::*)(char)' is not
a class, struct, or union type

The goal is that when the keypress signal is emitted, it will execute
the handler which will receive the char (key), test it, and emit its
signal (sig) if appropriate.

Any help would again be much appreciated, the short code follow, with
the problematic bind statement commented:

Thanks in advance,

Darren Hart

compile:  g++ test.cpp -o test -lboost_signals

// test.cpp ----------------------------------------------------
#include <iostream>
#include <boost/signal.hpp>
#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/bind/apply.hpp>

using namespace std;

struct widget
{
	boost::signal<bool ()> sig;
	boost::signal<bool (char)> keypress;
	bool test() 
	{ 
		cout << "widget::test() - sig empty: " << (sig.empty() ? "true" :
"false") << endl; 
		sig();
		return true;
	}
};

struct handler
{
	char key_;
	boost::signal<bool ()> sig;

	handler(char key) : key_(key) { }

	bool operator()(char key)
	{ 
		cout << "handler::operator() - received a " << key << endl;
		if (!sig.empty() && key == key_) 
		{
			cout << "\texecuting slot\n\t";
			sig();
		}
		cout << endl;
		return true;
	}
};

struct no_op
{
	bool operator()() { cout << "no_op::operator() - doing nothing" <<
endl; return true; }
	bool test() { cout << "no_op::test()" << endl; return true; }
};

int main()
{
	// instantiate two widgets
	widget widget_a;
	widget widget_b;

	// instanstiate the functions object (and test them)
	no_op no_op_;
	handler handler_a('A'); handler_a.sig.connect(no_op_);
	no_op_();
	handler_a('A');

	// connect the function objects to the widgets
	widget_a.sig.connect(no_op_);              

	// THE PROBLEM IS HERE - HOW DO I BIND TO handler_a.test(char) ?
	widget_b.keypress.connect( boost::bind(&handler::operator(),
&handler_a) );
	// END PROBLEM

	cout << "signalling widget_b.keypress('B')" << endl;
	widget_b.keypress('B'); // call the handler 3 times, but never execute
its slot

	cout << "\nsignalling widget_b.keypress('A')" << endl;
	widget_b.keypress('A'); // call the handler 3 times, executing the slot

	return 0;
}

Using Bind with Signals (version 2)

Darren Vincent Hart