[swift-evolution] [Pitch] Self.withoutSpecialization

[T.J. Usiyan]

I periodically kill all hope that we might get higher-kinded-types, just to
remain sane.

It's interesting that you would make them sound like a possibility though,
since Mr Widmann said something about you declaring them intractable for
some reason or another.

Well, this attempt to get them by hook or crook failed, but I won't let
that get me down. No. No I won't.

On Sat, Jul 2, 2016 at 11:40 AM, Dave Abrahams via swift-evolution <
swift-evolution at swift.org> wrote:

>
>
> on Fri Jul 01 2016, "T.J. Usiyan via swift-evolution" <
> swift-evolution at swift.org> wrote:
>
> > Bump
> >
> > On Fri, Jul 1, 2016 at 11:56 AM, T.J. Usiyan
> > <griotspeak at gmail.com> wrote:
> >
> >>
> >>
> >> ## The Issue
> >> Given
> >> ``` swift
> >> public protocol Zipper1D : CustomStringConvertible {
> >>     associatedtype Element
> >> }
> >> ```
> >>
> >> We can almost write a `flatMap`  which keeps the general identity of
> self
> >> and swaps out the Element in the output.
> >>
> >> ``` swift
> >> func flatMap<
> >>         NewElement, SegmentOfResult : Collection, Output : Zipper1D
> where
> >>         SegmentOfResult.Iterator.Element == NewElement, Output.Element
> ==
> >> NewElement>
> >>         (_ transform: @noescape (Element) throws -> SegmentOfResult)
> >> rethrows -> Output
> >> ```
> >>
> >> ## The Proposal
> >> I propose that we allow `Type.withoutSpecialization`
> >>
> >> ``` swift
> >> func flatMap<
> >>         NewElement, SegmentOfResult : Collection, Output : Zipper1D
> where
> >>         SegmentOfResult.Iterator.Element == NewElement, Output.Element
> ==
> >> NewElement, Output.withoutSpecialization == Self.withoutSepcialization>
> >>         (_ transform: @noescape (Element) throws -> SegmentOfResult)
> >> rethrows -> Output
> >> ```
> >>
> >>
> >> I recognize that generic protocols are another possible solution to this
> >> problem. I am pitching this because of how much closer this idea seems
> to
> >> being realized.
>
> The right answer to this problem is something called “higher-kinded
> types,” which are interesting to contemplate for the future, but most
> definitely out-of-scope at the moment.
>
> Cheers,
>
> --
> -Dave
>
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