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1 : // Boost next_prior.hpp header file ---------------------------------------//
2 :
3 : // (C) Copyright Dave Abrahams and Daniel Walker 1999-2003.
4 : // Copyright (c) Andrey Semashev 2017
5 : //
6 : // Distributed under the Boost Software License, Version 1.0.
7 : // (See accompanying file LICENSE_1_0.txt or copy at
8 : // http://www.boost.org/LICENSE_1_0.txt)
9 :
10 : // See http://www.boost.org/libs/utility for documentation.
11 :
12 : // Revision History
13 : // 13 Dec 2003 Added next(x, n) and prior(x, n) (Daniel Walker)
14 :
15 : #ifndef BOOST_NEXT_PRIOR_HPP_INCLUDED
16 : #define BOOST_NEXT_PRIOR_HPP_INCLUDED
17 :
18 : #include <iterator>
19 : #include <boost/config.hpp>
20 : #include <boost/core/enable_if.hpp>
21 : #include <boost/type_traits/has_plus.hpp>
22 : #include <boost/type_traits/has_plus_assign.hpp>
23 : #include <boost/type_traits/has_minus.hpp>
24 : #include <boost/type_traits/has_minus_assign.hpp>
25 : #include <boost/iterator/advance.hpp>
26 : #include <boost/iterator/reverse_iterator.hpp>
27 :
28 : namespace boost {
29 :
30 : // Helper functions for classes like bidirectional iterators not supporting
31 : // operator+ and operator-
32 : //
33 : // Usage:
34 : // const std::list<T>::iterator p = get_some_iterator();
35 : // const std::list<T>::iterator prev = boost::prior(p);
36 : // const std::list<T>::iterator next = boost::next(prev, 2);
37 :
38 : // Contributed by Dave Abrahams
39 :
40 : namespace next_prior_detail {
41 :
42 : // The trait attempts to detect if the T type is an iterator. Class-type iterators are assumed
43 : // to have the nested type iterator_category. Strictly speaking, this is not required to be the
44 : // case (e.g. a user can specialize iterator_traits for T without defining T::iterator_category).
45 : // Still, this is a good heuristic in practice, and we can't do anything better anyway.
46 : // Since C++17 we can test for iterator_traits<T>::iterator_category presence instead as it is
47 : // required to be only present for iterators.
48 : template< typename T, typename Void = void >
49 : struct is_iterator_class
50 : {
51 : static BOOST_CONSTEXPR_OR_CONST bool value = false;
52 : };
53 :
54 : template< typename T >
55 : struct is_iterator_class<
56 : T,
57 : typename enable_if_has_type<
58 : #if !defined(BOOST_NO_CXX17_ITERATOR_TRAITS)
59 : typename std::iterator_traits< T >::iterator_category
60 : #else
61 : typename T::iterator_category
62 : #endif
63 : >::type
64 : >
65 : {
66 : static BOOST_CONSTEXPR_OR_CONST bool value = true;
67 : };
68 :
69 : template< typename T >
70 : struct is_iterator :
71 : public is_iterator_class< T >
72 : {
73 : };
74 :
75 : template< typename T >
76 : struct is_iterator< T* >
77 : {
78 : static BOOST_CONSTEXPR_OR_CONST bool value = true;
79 : };
80 :
81 :
82 : template< typename T, typename Distance, bool HasPlus = has_plus< T, Distance >::value >
83 : struct next_plus_impl;
84 :
85 : template< typename T, typename Distance >
86 : struct next_plus_impl< T, Distance, true >
87 : {
88 : static T call(T x, Distance n)
89 : {
90 : return x + n;
91 : }
92 : };
93 :
94 : template< typename T, typename Distance, bool HasPlusAssign = has_plus_assign< T, Distance >::value >
95 : struct next_plus_assign_impl :
96 : public next_plus_impl< T, Distance >
97 : {
98 : };
99 :
100 : template< typename T, typename Distance >
101 : struct next_plus_assign_impl< T, Distance, true >
102 : {
103 : static T call(T x, Distance n)
104 : {
105 : x += n;
106 : return x;
107 : }
108 : };
109 :
110 : template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value >
111 : struct next_advance_impl :
112 : public next_plus_assign_impl< T, Distance >
113 : {
114 : };
115 :
116 : template< typename T, typename Distance >
117 : struct next_advance_impl< T, Distance, true >
118 : {
119 : static T call(T x, Distance n)
120 : {
121 : boost::iterators::advance(x, n);
122 : return x;
123 : }
124 : };
125 :
126 :
127 : template< typename T, typename Distance, bool HasMinus = has_minus< T, Distance >::value >
128 : struct prior_minus_impl;
129 :
130 : template< typename T, typename Distance >
131 : struct prior_minus_impl< T, Distance, true >
132 : {
133 : static T call(T x, Distance n)
134 : {
135 : return x - n;
136 : }
137 : };
138 :
139 : template< typename T, typename Distance, bool HasMinusAssign = has_minus_assign< T, Distance >::value >
140 : struct prior_minus_assign_impl :
141 : public prior_minus_impl< T, Distance >
142 : {
143 : };
144 :
145 : template< typename T, typename Distance >
146 : struct prior_minus_assign_impl< T, Distance, true >
147 : {
148 : static T call(T x, Distance n)
149 : {
150 : x -= n;
151 : return x;
152 : }
153 : };
154 :
155 : template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value >
156 : struct prior_advance_impl :
157 : public prior_minus_assign_impl< T, Distance >
158 : {
159 : };
160 :
161 : template< typename T, typename Distance >
162 : struct prior_advance_impl< T, Distance, true >
163 : {
164 : static T call(T x, Distance n)
165 : {
166 : // Avoid negating n to sidestep possible integer overflow
167 : boost::iterators::reverse_iterator< T > rx(x);
168 : boost::iterators::advance(rx, n);
169 : return rx.base();
170 : }
171 : };
172 :
173 : } // namespace next_prior_detail
174 :
175 : template <class T>
176 : inline T next(T x) { return ++x; }
177 :
178 : template <class T, class Distance>
179 : inline T next(T x, Distance n)
180 : {
181 : return next_prior_detail::next_advance_impl< T, Distance >::call(x, n);
182 : }
183 :
184 : template <class T>
185 0 : inline T prior(T x) { return --x; }
186 :
187 : template <class T, class Distance>
188 : inline T prior(T x, Distance n)
189 : {
190 : return next_prior_detail::prior_advance_impl< T, Distance >::call(x, n);
191 : }
192 :
193 : } // namespace boost
194 :
195 : #endif // BOOST_NEXT_PRIOR_HPP_INCLUDED
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