boost/signals2/last_value.hpp

   1 // last_value function object (documented as part of Boost.Signals)
   2
   3 // Copyright Frank Mori Hess 2007.
   4 // Copyright Douglas Gregor 2001-2003. Use, modification and
   5 // distribution is subject to the Boost Software License, Version
   6 // 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   7 // http://www.boost.org/LICENSE_1_0.txt)
   8
   9 // For more information, see http://www.boost.org
  10
  11 #ifndef BOOST_SIGNALS2_LAST_VALUE_HPP
  12 #define BOOST_SIGNALS2_LAST_VALUE_HPP
  13
  14 #include <boost/optional.hpp>
  15 #include <boost/signals2/detail/result_type_wrapper.hpp>
  16 #include <boost/throw_exception.hpp>
  17 #include <stdexcept>
  18
  19 namespace boost {
  20   namespace signals2 {
  21     class expired_slot;
  22
  23     // no_slots_error is thrown when we are unable to generate a return value
  24     // due to no slots being connected to the signal.
  25     class no_slots_error: public std::exception
  26     {
  27     public:
  28       virtual const char* what() const throw() {return "boost::signals2::no_slots_error";}
  29     };
  30
  31     template<typename T>
  32     class last_value {
  33     public:
  34       typedef T result_type;
  35
  36       template<typename InputIterator>
  37       T operator()(InputIterator first, InputIterator last) const
  38       {
  39         T * resolver = 0;
  40         if(first == last)
  41         {
  42           boost::throw_exception(no_slots_error());
  43         }
  44         optional<T> value;
  45         while (first != last)
  46         {
  47           try
  48           {
  49             value = *first;
  50           }
  51           catch(const expired_slot &) {}
  52           ++first;
  53         }
  54         if(value) return value.get();
  55         boost::throw_exception(no_slots_error());
  56       }
  57     };
  58
  59     template<>
  60     class last_value<void> {
  61     public:
  62       typedef detail::result_type_wrapper<void>::type result_type;
  63       template<typename InputIterator>
  64         result_type operator()(InputIterator first, InputIterator last) const
  65       {
  66         while (first != last)
  67         {
  68           try
  69           {
  70             *first;
  71           }
  72           catch(const expired_slot &) {}
  73           ++first;
  74         }
  75         return result_type();
  76       }
  77     };
  78   } // namespace signals2
  79 } // namespace boost
  80 #endif // BOOST_SIGNALS2_LAST_VALUE_HPP