> On Feb 13, 2017, at 4:40 PM, Maxim Veksler via swift-users
> <swift-users@swift.org> wrote:
>
> I'm trying to understand the signature of flapMap that allows it to "strip
> down" Optional from a type, when called on an Optional collection but remain
> same type when called on a non option collection.
>
> How would flatMap be implemented if would have been stand alone?
>
> This for ex. I can't get to compile:
>
> func flatMap<ElementOfResult, Element, T: Sequence>(on: T, _ transform:
> (Element) throws -> ElementOfResult?
> ) rethrows -> [ElementOfResult] {
> var result: [ElementOfResult] = []
> for element in on {
> if let newElement = try transform(element) {
> result.append(newElement)
> }
> }
> return result
> }
This doesn’t compile because there’s no relation between T.Element.Iterator and
Element. I think you want to remove the Element type parameter altogether, and
make the input type of flatMap into T.Element.Iterator.
Slava
>
>
> Additionally please see 2 related SO questions, for background.
>
> http://stackoverflow.com/q/42213656 <http://stackoverflow.com/q/42213656>
> http://stackoverflow.com/q/42214880 <http://stackoverflow.com/q/42214880>
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