API: Query no longer has iterator methods current(), first(), rewind(), next()
Using generators reduces the amount of boilerplate needed for this
code.
Turning it into an IteratorAggregate means that the iterator can be
re-created for each subsequent foreach call. This means that the
rewind() and seek() functionality can be discarded.
API: Query::seek() and Query::rewind() no longer return a value.
Although breaking an API inside a patch release may seem odd, this in
fact is correcting a long-standing bug in our implementation of
Iterator::rewind(), so I think it’s appropriate.
https://github.com/silverstripe/silverstripe-framework/issues/9097
