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
}
Additionally please see 2 related SO questions, for background.
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
···
On Feb 13, 2017, at 4:40 PM, Maxim Veksler via swift-users <swift-users@swift.org> wrote:
Additionally please see 2 related SO questions, for background.
swift - How flatMap API contract transforms Optional input to Non Optional result? - Stack Overflow
swift - flatMap does not filter out nil when ElementOfResult is inferred to be Optional - Stack Overflow
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