[swift-evolution] Adding Result to the Standard Library

[Tony Allevato]

Given that the Swift team is currently working on laying the groundwork for
asynchronous APIs using an async/await model, which would presumably tie
the throwing cases more naturally into the language than what is possible
using completion-closures today, are we sure that this wouldn't duplicate
any efforts there or be made obsolete through other means?

In other words, while Result<> can be a very useful foundational component
on its own, I think any proposal for it can't be made in isolation, but
very much needs to consider other asynchronous work going on in the
language.


On Thu, Nov 2, 2017 at 11:15 AM Jon Shier via swift-evolution <
swift-evolution at swift.org> wrote:

> You don’t lose it, it’s just behind `Error`. You can cast out whatever
> strong error type you need without having to bind an entire type to it
> generically. If getting a common error type out happens a lot, I usually
> add a convenience property to `Error` to do the cast for me. Plus, having
> to expose an entire new error wrapper is just a non starter for me and
> doesn’t seem necessary, given how Result is currently used in the community.
>
>
> Jon
>
>
> On Nov 2, 2017, at 2:12 PM, Dave DeLong <swift at davedelong.com> wrote:
>
> I think I’d personally rather see this done with a generic error as well,
> like:
>
> enum GenericResult<T, E: Error> {
> case success(T)
> case failure(E)
> }
>
> And a typealias:
>
> typealias Result<T> = GenericResult<T, AnyError>
>
> This would require an “AnyError” type to type-erase a specific Error, but
> I’ve come across many situations where a strongly-typed error is *incredibly
> *useful, and I’d be reluctant to see that thrown away.
>
> Dave
>
> On Nov 2, 2017, at 12:08 PM, Jon Shier via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Swift-Evolution:
> I’ve written a first draft of a proposal to add Result<T> to the standard
> library by directly porting the Result<T> type used in Alamofire to the
> standard library. I’d be happy to implement it (type and tests for free!)
> if someone could point me to the right place to do so. I’m not including it
> directly in this email, since it includes the full implementation and is
> therefore quite long. (Discourse, please!)
>
>
> https://github.com/jshier/swift-evolution/blob/master/proposals/0187-add-result-to-the-standard-library.md
>
>
> Thanks,
>
> Jon Shier
>
>
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