| // Boost next_prior.hpp header file ---------------------------------------// |
| |
| // (C) Copyright Dave Abrahams and Daniel Walker 1999-2003. |
| // Copyright (c) Andrey Semashev 2017 |
| // |
| // 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) |
| |
| // See http://www.boost.org/libs/utility for documentation. |
| |
| // Revision History |
| // 13 Dec 2003 Added next(x, n) and prior(x, n) (Daniel Walker) |
| |
| #ifndef BOOST_NEXT_PRIOR_HPP_INCLUDED |
| #define BOOST_NEXT_PRIOR_HPP_INCLUDED |
| |
| #include <iterator> |
| #include <boost/config.hpp> |
| #include <boost/core/enable_if.hpp> |
| #include <boost/type_traits/has_plus.hpp> |
| #include <boost/type_traits/has_plus_assign.hpp> |
| #include <boost/type_traits/has_minus.hpp> |
| #include <boost/type_traits/has_minus_assign.hpp> |
| #include <boost/iterator/advance.hpp> |
| #include <boost/iterator/reverse_iterator.hpp> |
| |
| namespace boost { |
| |
| // Helper functions for classes like bidirectional iterators not supporting |
| // operator+ and operator- |
| // |
| // Usage: |
| // const std::list<T>::iterator p = get_some_iterator(); |
| // const std::list<T>::iterator prev = boost::prior(p); |
| // const std::list<T>::iterator next = boost::next(prev, 2); |
| |
| // Contributed by Dave Abrahams |
| |
| namespace next_prior_detail { |
| |
| // The trait attempts to detect if the T type is an iterator. Class-type iterators are assumed |
| // to have the nested type iterator_category. Strictly speaking, this is not required to be the |
| // case (e.g. a user can specialize iterator_traits for T without defining T::iterator_category). |
| // Still, this is a good heuristic in practice, and we can't do anything better anyway. |
| // Since C++17 we can test for iterator_traits<T>::iterator_category presence instead as it is |
| // required to be only present for iterators. |
| template< typename T, typename Void = void > |
| struct is_iterator_class |
| { |
| static BOOST_CONSTEXPR_OR_CONST bool value = false; |
| }; |
| |
| template< typename T > |
| struct is_iterator_class< |
| T, |
| typename enable_if_has_type< |
| #if !defined(BOOST_NO_CXX17_ITERATOR_TRAITS) |
| typename std::iterator_traits< T >::iterator_category |
| #else |
| typename T::iterator_category |
| #endif |
| >::type |
| > |
| { |
| static BOOST_CONSTEXPR_OR_CONST bool value = true; |
| }; |
| |
| template< typename T > |
| struct is_iterator : |
| public is_iterator_class< T > |
| { |
| }; |
| |
| template< typename T > |
| struct is_iterator< T* > |
| { |
| static BOOST_CONSTEXPR_OR_CONST bool value = true; |
| }; |
| |
| |
| template< typename T, typename Distance, bool HasPlus = has_plus< T, Distance >::value > |
| struct next_plus_impl; |
| |
| template< typename T, typename Distance > |
| struct next_plus_impl< T, Distance, true > |
| { |
| static T call(T x, Distance n) |
| { |
| return x + n; |
| } |
| }; |
| |
| template< typename T, typename Distance, bool HasPlusAssign = has_plus_assign< T, Distance >::value > |
| struct next_plus_assign_impl : |
| public next_plus_impl< T, Distance > |
| { |
| }; |
| |
| template< typename T, typename Distance > |
| struct next_plus_assign_impl< T, Distance, true > |
| { |
| static T call(T x, Distance n) |
| { |
| x += n; |
| return x; |
| } |
| }; |
| |
| template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value > |
| struct next_advance_impl : |
| public next_plus_assign_impl< T, Distance > |
| { |
| }; |
| |
| template< typename T, typename Distance > |
| struct next_advance_impl< T, Distance, true > |
| { |
| static T call(T x, Distance n) |
| { |
| boost::iterators::advance(x, n); |
| return x; |
| } |
| }; |
| |
| |
| template< typename T, typename Distance, bool HasMinus = has_minus< T, Distance >::value > |
| struct prior_minus_impl; |
| |
| template< typename T, typename Distance > |
| struct prior_minus_impl< T, Distance, true > |
| { |
| static T call(T x, Distance n) |
| { |
| return x - n; |
| } |
| }; |
| |
| template< typename T, typename Distance, bool HasMinusAssign = has_minus_assign< T, Distance >::value > |
| struct prior_minus_assign_impl : |
| public prior_minus_impl< T, Distance > |
| { |
| }; |
| |
| template< typename T, typename Distance > |
| struct prior_minus_assign_impl< T, Distance, true > |
| { |
| static T call(T x, Distance n) |
| { |
| x -= n; |
| return x; |
| } |
| }; |
| |
| template< typename T, typename Distance, bool IsIterator = is_iterator< T >::value > |
| struct prior_advance_impl : |
| public prior_minus_assign_impl< T, Distance > |
| { |
| }; |
| |
| template< typename T, typename Distance > |
| struct prior_advance_impl< T, Distance, true > |
| { |
| static T call(T x, Distance n) |
| { |
| // Avoid negating n to sidestep possible integer overflow |
| boost::iterators::reverse_iterator< T > rx(x); |
| boost::iterators::advance(rx, n); |
| return rx.base(); |
| } |
| }; |
| |
| } // namespace next_prior_detail |
| |
| template <class T> |
| inline T next(T x) { return ++x; } |
| |
| template <class T, class Distance> |
| inline T next(T x, Distance n) |
| { |
| return next_prior_detail::next_advance_impl< T, Distance >::call(x, n); |
| } |
| |
| template <class T> |
| inline T prior(T x) { return --x; } |
| |
| template <class T, class Distance> |
| inline T prior(T x, Distance n) |
| { |
| return next_prior_detail::prior_advance_impl< T, Distance >::call(x, n); |
| } |
| |
| } // namespace boost |
| |
| #endif // BOOST_NEXT_PRIOR_HPP_INCLUDED |