Reverse inserter

[NDos Dannyu]

std::inserter uses the plain iterator of the container, so it can't be used to insert elements in reverse order.

std::insert_iterator can't be passed to std::make_reverse_iterator, because it has void member types.

So I suggest adding reverse inserter, Like this:

namespace std {

    template <class Container> class reverse_insert_iterator {

    private:

        typedef typename Container::iterator __i;

    protected:

        Container *container;

        __i iter;

    public:

        typedef Container container_type;

        typedef void value_type, difference_type, pointer, reference;

        typedef output_iterator_tag iterator_category;

        explicit reverse_insert_iterator(Container &c, __i i) noexcept :

            container(&c), iter(make_reverse_iterator(i)) {}

        reverse_insert_iterator &operator = (const typename Container::value_type &value) {

            iter = container->insert(iter, value);

            // Note that iter isn't increased here and thus simulates reverse insertion.

            return *this;

        }

        reverse_insert_iterator &operator = (typename Container::value_type &&value) {

            iter = container->insert(iter, value);

            // Ditto.

            return *this;

        }

        reverse_insert_iterator &operator * ()  noexcept {

            return *this;

        }

        reverse_insert_iterator &operator ++ () noexcept {

            return *this;

        }

        reverse_insert_iterator &operator ++ (int) noexcept {

            return *this;

        }

    };

    template <class Container>

    reverse_insert_iterator<Container> reverse_inserter(Container &c, typename Container::iterator i) noexcept {

        return reverse_insert_iterator<Container>(c, i);

    }

}

[Arthur O'Dwyer]

On Saturday, March 5, 2016 at 9:16:17 PM UTC-8, NDos Dannyu wrote:

std::inserter uses the plain iterator of the container, so it can't be used to insert elements in reverse order.

I imagine that most of the use-cases for such a thing could be handled with std::front_inserter.

http://en.cppreference.com/w/cpp/iterator/front_insert_iterator

http://en.cppreference.com/w/cpp/iterator/front_inserter

IIUC, you're looking specifically for a way to

- insert elements from the range B...E

- into an existing (possibly non-empty) container

- not at the front, but rather somewhere in the middle (otherwise front_inserter would fit the bill)

- where the inserted elements must wind up in reverse order

- where for some reason inserting the elements "in non-reversed order, from the range make_reverse_iterator(E)...make_reverse_iterator(B)" would be unacceptable

and you really want to use a standard algorithm for this instead of writing a for loop.

I suspect that it wouldn't be worth adding to the STL's zoo of weird iterator types, given that Ranges are going to arrive soon. How does Ranges handle insertion?

my $.02,

Arthur