// Boost.Signals library // Copyright Douglas Gregor 2001-2003. Use, modification and // distribution is subject to the Boost Software License, Version // 1.0. (See accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) // For more information, see http://www.boost.org #include <boost/signals/signal2.hpp> #include <iostream> template<typename T> struct first_positive { typedef T result_type; template<typename InputIterator> T operator()(InputIterator first, InputIterator last) const { while (first != last && !(*first > 0)) { ++first; } return (first == last) ? 0 : *first; } }; template<typename T> struct noisy_divide { typedef T result_type; T operator()(const T& x, const T& y) const { std::cout << "Dividing " << x << " and " << y << std::endl; return x/y; } }; int main() { boost::signal2<int, int, int, first_positive<int> > sig_positive; sig_positive.connect(std::plus<int>()); sig_positive.connect(std::multiplies<int>()); sig_positive.connect(std::minus<int>()); sig_positive.connect(noisy_divide<int>()); assert(sig_positive(3, -5) == 8); // returns 8, but prints nothing return 0; }