[swift-evolution] [Pitch] Non-class type requirements on protocols (eg : struct, : enum)

T.J. Usiyan griotspeak at gmail.com
Sat Oct 22 14:56:00 CDT 2016

Thanks for the heads up! It wasn't just meant for you. Use of a generic
Result type is one of my motivating cases.

1. If multiple libraries declare a generic type like that, converting
between them becomes a pain.
2. Specific result types are useful and appropriate in many, if not most,
3. protocols and retroactive conformance could make this less challenging

On Sat, Oct 22, 2016 at 3:42 PM, David Sweeris <davesweeris at mac.com> wrote:

> Was not sending your reply only to me and not the list intentional? It’s
> fine either way, I was just about to send this to the list when I realized
> you’d only sent your reply to me, and I don’t want quote you somewhere if
> you intentionally didn’t post there.
> On Oct 22, 2016, at 1:39 PM, T.J. Usiyan <griotspeak at gmail.com> wrote:
> I would actually hope otherwise. A real benefit of enums is compile time
> guarantees. I am looking for a generic means to represent and handle a set
> of possible outcomes. Not in the hopes of making everything fully generic
> but lessening the redundant parts of dealing with, for example, Result
> types.
> I think you can do that now...
> enum Result<Payload> {
>     case success(Payload)
>     case failure(Error)
> }
> Then in your function…
> func foo<T> (r: Result<T>) {
>     ...
>     switch r {
>     case .success(let p): ...
>     case .failure(let e): ...
>     }
>     ...
> }
> Or am I just not understanding you?
> - Dave Sweeris
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