public void foreach_member (ObjectForeach func)
Iterates over all members of this and calls
func on each one of them.
It is safe to change the value of a Node of the this
from within the iterator
func, but it is not safe to add or remove members from the this.
The order in which the this members are iterated is the insertion order.
the function to be called on each member
data to be passed to the function