[swift-evolution] Adding Result to the Standard Library

[Jon Shier]

	That’s been an argument against Result for 2 years now. The usefulness of the type, even outside of whatever asynchronous language support the core team comes up with, perhaps this year, perhaps next year, is still very high. Even as something that just wraps throwing functions, or otherwise exists as a local, synchronous value, it’s still very useful as way to encapsulate the value/error pattern. That pattern will likely never go away. Additionally, having the Result type in the standard library removes a source of conflict between all other Result implementations, which are becoming more common.

> On Nov 2, 2017, at 2:26 PM, Tony Allevato <tony.allevato at gmail.com> wrote:
> 
> 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 <mailto: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 <mailto: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 <mailto: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 <https://github.com/jshier/swift-evolution/blob/master/proposals/0187-add-result-to-the-standard-library.md>
>>> 
>>> 
>>> Thanks, 
>>> 
>>> Jon Shier
>>> 
>>> 
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>> 
> 
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