guarantees that this iterator can be used as the end of a range, without
danger of problems due to concurrent calls to
on the map. If
anchor() has not been called for a given
iterator, then comparisons
of that iterator with another will throw
the node referenced by that iterator has been deleted from the map.
This is of specialized use: since the map is unordered, iteration across
subranges is tricky, as the order of elements is not guaranteed. The
iterator returned from
end() is always an anchor.
Anchors the current node.
std::bad_alloc if the memory required
to store the anchor information could not be allocated.