boost/libs/signals/example/first_positive.cpp

   1 // Boost.Signals library
   2
   3 // Copyright Douglas Gregor 2001-2003. Use, modification and
   4 // distribution is subject to the Boost Software License, Version
   5 // 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   6 // http://www.boost.org/LICENSE_1_0.txt)
   7
   8 // For more information, see http://www.boost.org
   9
  10 #include <boost/signals/signal2.hpp>
  11 #include <iostream>
  12
  13 template<typename T>
  14 struct first_positive {
  15   typedef T result_type;
  16
  17   template<typename InputIterator>
  18   T operator()(InputIterator first, InputIterator last) const
  19   {
  20     while (first != last && !(*first > 0)) { ++first; }
  21     return (first == last) ? 0
  22                            : *first;
  23   }
  24 };
  25
  26 template<typename T>
  27 struct noisy_divide {
  28   typedef T result_type;
  29
  30   T operator()(const T& x, const T& y) const
  31   {
  32     std::cout << "Dividing " << x << " and " << y << std::endl;
  33     return x/y;
  34   }
  35 };
  36
  37 int main()
  38 {
  39   boost::signal2<int, int, int, first_positive<int> > sig_positive;
  40   sig_positive.connect(std::plus<int>());
  41   sig_positive.connect(std::multiplies<int>());
  42   sig_positive.connect(std::minus<int>());
  43   sig_positive.connect(noisy_divide<int>());
  44
  45   assert(sig_positive(3, -5) == 8); // returns 8, but prints nothing
  46
  47   return 0;
  48 }