boost/last_value.hpp

   1 // last_value function object (documented as part of Boost.Signals)
   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/libs/signals
   9
  10 #ifndef BOOST_LAST_VALUE_HPP
  11 #define BOOST_LAST_VALUE_HPP
  12
  13 #include <cassert>
  14 #include <boost/config.hpp>
  15
  16 namespace boost {
  17   template<typename T>
  18   struct last_value {
  19     typedef T result_type;
  20
  21     template<typename InputIterator>
  22     T operator()(InputIterator first, InputIterator last) const
  23     {
  24       assert(first != last);
  25       T value = *first++;
  26       while (first != last)
  27         value = *first++;
  28       return value;
  29     }
  30   };
  31
  32   template<>
  33   struct last_value<void> {
  34 #ifdef BOOST_NO_VOID_RETURNS
  35     struct unusable {};
  36
  37   public:
  38     typedef unusable result_type;
  39 #else
  40   public:
  41     typedef void result_type;
  42 #endif // BOOST_NO_VOID_RETURNS
  43
  44     template<typename InputIterator>
  45     result_type
  46     operator()(InputIterator first, InputIterator last) const
  47     {
  48       while (first != last)
  49         *first++;
  50       return result_type();
  51     }
  52   };
  53 }
  54 #endif // BOOST_SIGNALS_LAST_VALUE_HPP