include/nlohmann/detail/iterators/json_reverse_iterator.hpp

#pragma once

#include <cstddef> // ptrdiff_t
#include <iterator> // reverse_iterator
#include <utility> // declval

namespace nlohmann
{
namespace detail
{
//////////////////////
// reverse_iterator //
//////////////////////

/*!
@brief a template for a reverse iterator class

@tparam Base the base iterator type to reverse. Valid types are @ref
iterator (to create @ref reverse_iterator) and @ref const_iterator (to
create @ref const_reverse_iterator).

@requirement The class satisfies the following concept requirements:
-
[BidirectionalIterator](http://en.cppreference.com/w/cpp/concept/BidirectionalIterator):
  The iterator that can be moved can be moved in both directions (i.e.
  incremented and decremented).
- [OutputIterator](http://en.cppreference.com/w/cpp/concept/OutputIterator):
  It is possible to write to the pointed-to element (only if @a Base is
  @ref iterator).

@since version 1.0.0
*/
template<typename Base>
class json_reverse_iterator : public std::reverse_iterator<Base>
{
  public:
    using difference_type = std::ptrdiff_t;
    /// shortcut to the reverse iterator adapter
    using base_iterator = std::reverse_iterator<Base>;
    /// the reference type for the pointed-to element
    using reference = typename Base::reference;

    /// create reverse iterator from iterator
    json_reverse_iterator(const typename base_iterator::iterator_type& it) noexcept
        : base_iterator(it) {}

    /// create reverse iterator from base class
    json_reverse_iterator(const base_iterator& it) noexcept : base_iterator(it) {}

    /// post-increment (it++)
    json_reverse_iterator const operator++(int)
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator++(1));
    }

    /// pre-increment (++it)
    json_reverse_iterator& operator++()
    {
        return static_cast<json_reverse_iterator&>(base_iterator::operator++());
    }

    /// post-decrement (it--)
    json_reverse_iterator const operator--(int)
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator--(1));
    }

    /// pre-decrement (--it)
    json_reverse_iterator& operator--()
    {
        return static_cast<json_reverse_iterator&>(base_iterator::operator--());
    }

    /// add to iterator
    json_reverse_iterator& operator+=(difference_type i)
    {
        return static_cast<json_reverse_iterator&>(base_iterator::operator+=(i));
    }

    /// add to iterator
    json_reverse_iterator operator+(difference_type i) const
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator+(i));
    }

    /// subtract from iterator
    json_reverse_iterator operator-(difference_type i) const
    {
        return static_cast<json_reverse_iterator>(base_iterator::operator-(i));
    }

    /// return difference
    difference_type operator-(const json_reverse_iterator& other) const
    {
        return base_iterator(*this) - base_iterator(other);
    }

    /// access to successor
    reference operator[](difference_type n) const
    {
        return *(this->operator+(n));
    }

    /// return the key of an object iterator
    auto key() const -> decltype(std::declval<Base>().key())
    {
        auto it = --this->base();
        return it.key();
    }

    /// return the value of an iterator
    reference value() const
    {
        auto it = --this->base();
        return it.operator * ();
    }
};
}
}