A list of initializer functions (with no arguments)
for iterators.
get_next
A function for retrieving next item for an iterator
argument; it assumes that the iterator returns NULL
when finished.
sspace
elements to be used (a list of vectors)
Value
A function that returns list of values, and stops with
"StopIteration" message when finished, so that it can be used with the
iterators::iter() function to create an iterator that works with foreach.