random_access_iterator(
random_access_iterator<OtherIterator, Category> const& other
, typename boost::enable_if<
boost::is_convertible<OtherIterator, Iterator>
, enabler
>::type = enabler()
)
: random_access_iterator::iterator_adaptor_(other.base()) {}
constexpr Iter base(random_access_iterator<Iter> i) { return i.base(); }