Re: [swift-users] How flatMap's signature is able to translate from Optional to [Type]?

[Slava Pestov via swift-users]

> On Feb 13, 2017, at 4:40 PM, Maxim Veksler via swift-users 
>  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(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/42214880 
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[swift-users] How flatMap's signature is able to translate from Optional to [Type]?

[Maxim Veksler via swift-users]

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(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.

http://stackoverflow.com/q/42213656
http://stackoverflow.com/q/42214880
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