/* * * (C) Copyright John Maddock 1999-2005. * Use, modification and distribution are subject to 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) * * This file provides some example of type_traits usage - * by "optimising" various algorithms: * * opt::iter_swap - uses type_traits to determine whether the iterator is a proxy * in which case it uses a "safe" approach, otherwise calls swap * on the assumption that swap may be specialised for the pointed-to type. * */ #include <iostream> #include <typeinfo> #include <algorithm> #include <iterator> #include <vector> #include <memory> #include <boost/test/included/prg_exec_monitor.hpp> #include <boost/type_traits.hpp> using std::cout; using std::endl; using std::cin; namespace opt{ // // iter_swap: // tests whether iterator is a proxy iterator or not, and // uses optimal form accordingly: // namespace detail{ template <typename I> static void do_swap(I one, I two, const boost::false_type&) { typedef typename std::iterator_traits<I>::value_type v_t; v_t v = *one; *one = *two; *two = v; } template <typename I> static void do_swap(I one, I two, const boost::true_type&) { using std::swap; swap(*one, *two); } } template <typename I1, typename I2> inline void iter_swap(I1 one, I2 two) { // // See is both arguments are non-proxying iterators, // and if both iterator the same type: // typedef typename std::iterator_traits<I1>::reference r1_t; typedef typename std::iterator_traits<I2>::reference r2_t; typedef boost::integral_constant<bool, ::boost::is_reference<r1_t>::value && ::boost::is_reference<r2_t>::value && ::boost::is_same<r1_t, r2_t>::value> truth_type; detail::do_swap(one, two, truth_type()); } }; // namespace opt int cpp_main(int argc, char* argv[]) { // // testing iter_swap // really just a check that it does in fact compile... std::vector<int> v1; v1.push_back(0); v1.push_back(1); std::vector<bool> v2; v2.push_back(0); v2.push_back(1); opt::iter_swap(v1.begin(), v1.begin()+1); opt::iter_swap(v2.begin(), v2.begin()+1); return 0; }