> On Apr 12, 2016, at 11:53 AM, Jens Alfke via swift-users
> <[email protected]> wrote:
>
> What should one do, when implementing a Generator, if the underlying data
> source can experience errors? Generator.next isn’t allowed to throw, only to
> return nil at the end of the sequence.
>
> The only idea I can think of is to add an `error` property to my Generator
> implementation, and request that the caller check it after the iteration
> ends, and/or a `checkForError()` method that can throw an error if there is
> one:
> var q: Query = db.query(…)
> for (row in q) { … }
> q.checkForError()
>
> As the example implies, this problem comes up when creating Swift bindings
> for database iterators/cursors. Generator is the obvious protocol to
> implement, especially since without it you don’t get the idiomatic for/in
> loop, but the `next` method does have to hit the database, so it has the
> possibility of I/O errors.
What I might do is use a block to make sure you can't forget the
`checkForError()` method:
let query = db.query(…)
try query.withResults { results in
// `results` is a SequenceType you can iterate over.
// You can only get at it by calling `withResults` on a Query,
and it becomes invalid once
// `withResults` returns.
// If `results` encounters an error, it terminates early.
for row in results {
// Use your row
}
}
--
Brent Royal-Gordon
Architechies
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