Bind a boost signal with phoenix bind - c++

Question

I am using boost spirit qi to parse inbound data then dispatch the correct functionality depending on it's content.
I am using boost::signals to manage the callbacks; my problem is that I don't seem to be able to use phoenix bind with the boost signals.
Consider the following test case:
#include <boost/signals.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_bind.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <iostream>
void f(int i) {
std::cout << i << '\n';
}
int main() {
boost::signal<void(int)> sig;
sig.connect(f);
std::string s="123";
auto first=s.cbegin(), last=s.cend();
boost::spirit::qi::parse(
first, last,
(
boost::spirit::qi::int_
[
boost::phoenix::bind(sig, boost::spirit::qi::_1)
]
)
);
}
This doesn't compile, spitting out a wall of errors.
Note that if I replace the phoenix bind line with
boost::phoenix::bind(&f, boost::spirit::qi::_1)
it works as expected (however due to the larger design of the program this isn't possible).
Thanks in advance.

Answer 1

As noted by Igor R. in the comments, your original error was due to the fact that phoenix::bind copies its arguments by default and boost::signals are non-copyable. When you use phoenix::ref to solve that, another error emerges, this one caused by Boost.Phoenix v2's inability to find the returned type. This can also be easily solved by defining BOOST_SPIRIT_USE_PHOENIX_V3.
#include <boost/signals.hpp>
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_bind.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <iostream>
void f(int i) {
std::cout << i << '\n';
}
int main() {
boost::signal<void(int)> sig;
sig.connect(f);
std::string s="123";
auto first=s.cbegin(), last=s.cend();
boost::spirit::qi::parse(
first, last,
(
boost::spirit::qi::int_
[
boost::phoenix::bind(boost::phoenix::ref(sig), boost::spirit::qi::_1)
]
)
);
}