1
2 /*
3 *
4 * (C) Copyright John Maddock 1999-2005.
5 * Use, modification and distribution are subject to the
6 * Boost Software License, Version 1.0. (See accompanying file
7 * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
8 *
9 * This file provides some example of type_traits usage -
10 * by "optimising" various algorithms:
11 *
12 * opt::iter_swap - uses type_traits to determine whether the iterator is a proxy
13 * in which case it uses a "safe" approach, otherwise calls swap
14 * on the assumption that swap may be specialised for the pointed-to type.
15 *
16 */
17
18 #include <iostream>
19 #include <typeinfo>
20 #include <algorithm>
21 #include <iterator>
22 #include <vector>
23 #include <memory>
24
25 #include <boost/test/included/prg_exec_monitor.hpp>
26 #include <boost/type_traits.hpp>
27
28 using std::cout;
29 using std::endl;
30 using std::cin;
31
32 namespace opt{
33
34 //
35 // iter_swap:
36 // tests whether iterator is a proxy iterator or not, and
37 // uses optimal form accordingly:
38 //
39 namespace detail{
40
41 template <typename I>
do_swap(I one,I two,const boost::false_type &)42 static void do_swap(I one, I two, const boost::false_type&)
43 {
44 typedef typename std::iterator_traits<I>::value_type v_t;
45 v_t v = *one;
46 *one = *two;
47 *two = v;
48 }
49 template <typename I>
do_swap(I one,I two,const boost::true_type &)50 static void do_swap(I one, I two, const boost::true_type&)
51 {
52 using std::swap;
53 swap(*one, *two);
54 }
55
56 }
57
58 template <typename I1, typename I2>
iter_swap(I1 one,I2 two)59 inline void iter_swap(I1 one, I2 two)
60 {
61 //
62 // See is both arguments are non-proxying iterators,
63 // and if both iterator the same type:
64 //
65 typedef typename std::iterator_traits<I1>::reference r1_t;
66 typedef typename std::iterator_traits<I2>::reference r2_t;
67
68 typedef boost::integral_constant<bool,
69 ::boost::is_reference<r1_t>::value
70 && ::boost::is_reference<r2_t>::value
71 && ::boost::is_same<r1_t, r2_t>::value> truth_type;
72
73 detail::do_swap(one, two, truth_type());
74 }
75
76
77 }; // namespace opt
78
cpp_main(int argc,char * argv[])79 int cpp_main(int argc, char* argv[])
80 {
81 //
82 // testing iter_swap
83 // really just a check that it does in fact compile...
84 std::vector<int> v1;
85 v1.push_back(0);
86 v1.push_back(1);
87 std::vector<bool> v2;
88 v2.push_back(0);
89 v2.push_back(1);
90 opt::iter_swap(v1.begin(), v1.begin()+1);
91 opt::iter_swap(v2.begin(), v2.begin()+1);
92
93 return 0;
94 }
95
96
97
98