问如何将DRY原则应用于C++中的迭代器？(迭代器、const_iterator、reverse_iterator、const_reverse_iterator)

EN

#include <type_traits>

template<typename Container, bool forward>
class iterator_base
{
public:
    using value_type =
        typename std::conditional<std::is_const<Container>::value,
                                 const typename Container::value_type,
                                 typename Container::value_type>::type;

    iterator_base() { }

    // For conversions from iterator to const_iterator.
    template<typename U>
    iterator_base(const iterator_base<U, forward>& other)
    : c(other.c)
    {
        // ....
    }

    value_type& operator*() const
    {
        // ...
    }

    iterator_base& operator++()
    {
        if (forward)
        {
            // ...
        }
        else
        {
            // ...
        }
    }

    iterator_base& operator++(int)
    {
        iterator_base copy(*this);
        ++*this;
        return copy;
    }

private:
    Container* c = nullptr;
    // ...
};

using iterator = iterator_base<self_type, true>;
using const_iterator = iterator_base<const self_type, true>;

using reverse_iterator = iterator_base<self_type, false>;
using const_reverse_iterator = iterator_base<const self_type, false>;