Algorithms from BoostCon 'Library in a week'

[SVN r45440]

include/boost/algorithm/select.hpp

@@ -0,0 +1,54 @@
+/* 
+   Copyright (c) Marshall Clow 2008.
+
+   Distributed under 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)
+
+   Implemented by SGI in their STL implementation
+   This implemnetation is based on interprocess::detail::select1st by Ion Gaztanaga.
+
+  Revision history:
+   06 May 2008 mtc First version - as part of BoostCon 2008
+*/
+
+#ifndef BOOST_ALGORITHM_SELECT_HPP
+#define BOOST_ALGORITHM_SELECT_HPP
+
+
+/// \file select.hpp
+/// \brief Boost implementation select1st and select2nd.
+/// \author Marshall Clow
+
+namespace boost { namespace algorithm {
+
+/// \fn select1st
+/// \brief Unary function that returns the first element of a std::pair
+/// 
+/// \param p     The pair.
+/// \return      p.first
+///
+///
+  template <class Pair>
+  struct select1st : public std::unary_function<Pair, typename Pair::first_type> 
+  {
+     const typename Pair::first_type& operator()(const Pair& p) const { return p.first; }
+           typename Pair::first_type& operator()(      Pair& p) const { return p.first; }
+  };
+
+/// \fn select2nd
+/// \brief Unary function that returns the first element of a std::pair
+/// 
+/// \param p     The pair.
+/// \return      p.first
+///
+///
+  template <class Pair>
+  struct select2nd : public std::unary_function<Pair, typename Pair::second_type> 
+  {
+     const typename Pair::second_type& operator()(const Pair& p) const { return p.second; }
+           typename Pair::second_type& operator()(      Pair& p) const { return p.second; }
+  };
+
+}} // namespace boost & algorithm
+
+#endif // BOOST_ALGORITHM_SELECT_HPP