[swift-evolution] Add an ifPresent function to Optional

[Howard Lovatt]

RE: map etc. returning Array

You could currently return AnyCollection though, and that would then let
Optional.map also return AnyCollection.

There is also talk in completing generics so that map could return
Any<CollectionType where Element == Element> which would be even better
than AnyCollection since a wrapper is removed.

  -- Howard.

On 15 March 2016 at 12:29, Dmitri Gribenko via swift-evolution <
swift-evolution at swift.org> wrote:

> On Mon, Mar 14, 2016 at 5:51 PM,  <davesweeris at mac.com> wrote:
> >
> > On Mar 14, 2016, at 5:51 PM, Dmitri Gribenko via swift-evolution
> > <swift-evolution at swift.org> wrote:
> >
> > Optional.map returns an Optional.
> >
> > Array.map returns an Array.
> > Set.map returns an Array.
> > <any other collection>.map returns an Array.
> >
> > I can't say that it is not valid to think about an Optional as a tiny
> > collection, but as implemented in Swift, .map() does objectively
> > behave differently...
> >
> > That behavior is, at least partially, because protocols don’t currently
> > support this:
> > protocol CollectionType {
> >     typealias T
> >     func map<U>(transform: T->U) -> Self<U> // error: Cannot specialize
> > non-generic type 'Self'
> > }
>
> This feature is called higher-kinded types, and it is not planned for
> design or implementation in the near future.
>
> > I *think* I remember reading on here somewhere that the intent is to
> change
> > map and flatMap to return “Self<U>" pretty much as soon as the language
> > supports it.
>
> As a standard library engineer I can with certainty that this is not
> the plan.  We like the current formulation of map() that returns an
> Array.
>
>
> https://github.com/apple/swift/blob/master/docs/StdlibRationales.rst#high-order-functions-on-collections-return-arrays
>
> I don't think that having HKTs in the language would change the rationale.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
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