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/core/no_exceptions_support.hpp>
15 #include <boost/optional.hpp>
16 #include <boost/signals2/expired_slot.hpp>
17 #include <boost/throw_exception.hpp>
18 #include <stdexcept>
19 
20 namespace boost {
21   namespace signals2 {
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:
what() const28       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>
operator ()(InputIterator first,InputIterator last) const37       T operator()(InputIterator first, InputIterator last) const
38       {
39         if(first == last)
40         {
41           boost::throw_exception(no_slots_error());
42         }
43         optional<T> value;
44         while (first != last)
45         {
46           BOOST_TRY
47           {
48             value = *first;
49           }
50           BOOST_CATCH(const expired_slot &) {}
51           BOOST_CATCH_END
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 void result_type;
63       template<typename InputIterator>
operator ()(InputIterator first,InputIterator last) const64         result_type operator()(InputIterator first, InputIterator last) const
65       {
66         while (first != last)
67         {
68           BOOST_TRY
69           {
70             *first;
71           }
72           BOOST_CATCH(const expired_slot &) {}
73           BOOST_CATCH_END
74           ++first;
75         }
76         return;
77       }
78     };
79   } // namespace signals2
80 } // namespace boost
81 #endif // BOOST_SIGNALS2_LAST_VALUE_HPP
82