Folds func over the elements of iter.
That is to say, func will be called as func (object, ret, user_data) for each object
in this. The normal use of this procedure is to accumulate the results of operating on the objects in
ret.
This procedure can be used (and is used internally) to implement the @foreach and find_custom operations.
The fold will proceed as long as func returns true. When the iterator has no more arguments,
DONE will be returned. If func returns false, the
fold will stop, and OK will be returned. Errors or resyncs will cause fold to
return ERROR or
RESYNC as appropriate.
The iterator will not be freed.
| this |
The Iterator to fold over |
| func |
the fold function |
| ret |
the seed value passed to the fold function |
| user_data |
user data passed to the fold function |