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Editing: next_prior.hpp
// 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
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