[swift-evolution] Adding Result to the Standard Library

[Wallacy]

If my memory does not fail, there has also been a discussion about adding a
"payload" to the optional types that fit into that context.

Something like:

//Current
enum Optional<T>{
 case Some(T)
 case None
}

// Adding
enum Optional<T,Error>{
 case Some(T)
 case None(Error)
 //Maybe adding support functions too
}

And some compiler magics to make Optional<T,Error> always to be convertible
to Optional<T> (losing Error info of course)... And support to optional
chaining and other current optional tricks.

In this case:

let some = try? foo() // some is Optional<T,Error>

some?.bar() // works

And we can do:

switch some{
   case .Some(let value):
   // ...
  case .None(let error):
  //
}

Other idea was presented in Swift 2/3 time frame was just:

enum Optional<T>{
 case Some(T)
 case None
 var payload:Any!
}


I am not saying that this is the best way, but in fact it is better to
think about what we can do to improve the current scenario, than to
introduce another type that may or may not make everything more confusing.


Em sex, 3 de nov de 2017 às 09:13, Benjamin G via swift-evolution <
swift-evolution at swift.org> escreveu:

> Just an idea for the type declaration :
>
> Why not use the same ? as Optional, but with the type of the error behind :
>
> Such as
>
> var x: Int?Error
>
> Optional Int (Int?) would be seen a special case of Result where the error
> type is nil.
>
> The advantage of this syntax is that it would let us specify the type of
> the error if we want it.
>
>
> On Fri, Nov 3, 2017 at 11:45 AM, Nick Keets via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Right, to me there is not a lot of value in adding Result as it exists in
>> AlamoFire. We will (eventually) use the Swift Package Manager for things
>> like this. The value would be in integrating it like Optionals. e.g. (using
>> a strawman symbol)
>>
>>     var x: Int‽ = 5
>>     var y: Int‽ = anErrorValue
>>
>>     func foo() -> Int‽ { ... }
>>
>>     if let x = foo() {
>>         // x is Int
>>     } else {
>>         // somehow access the error
>>     }
>>
>>     guard let x = foo() else {
>>         // Again somehow access the error
>>     }
>>
>>     func bar() throws -> String { ... }
>>     let x = try‽ bar()   // x is String‽
>>     let y = x!  // y is String
>>
>>     // Possibly even make it throw? (just using a random symbol again)
>>     let z = try x¡
>>
>>
>> On Fri, Nov 3, 2017 at 2:02 AM, Xiaodi Wu via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>> This is clearly a fine addition to the standard library; even Swift's
>>> Error Handling Rationale (
>>> https://github.com/apple/swift/blob/master/docs/ErrorHandlingRationale.rst)
>>> mentions such an addition
>>>
>>> What separates standard library types from other types is that they have
>>> language level support, and the wrapping and unwrapping syntax here could
>>> definitely benefit from it (`.unwrap()`--which should be `.unwrapped()`
>>> incidentally--is so much less elegant in comparison to `?` and `!` for
>>> optionals (not that `Result` should use the exact such syntax for a
>>> distinct operation)). It would be a shame to transpose a third-party
>>> `Result` to the standard library without considering if any such tweaks
>>> would substantially improve ergonomics, interconversion with Optional and
>>> throws, etc.
>>>
>>>
>>> On Thu, Nov 2, 2017 at 1:08 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
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>
>>>>
>>>
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>>>
>>>
>>
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>>
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