[swift-evolution] guard let x = x

[Warren Gavin]

I like the simplicity of 'unwrap' solving the issue of repetition, but it
assumes 'let' in each example I've seen. 'guard var x = x' may not be
written as frequently, but it is still valid. I can't imagine the intention
would be that 'unwrap' is only for 'let'



On Sun, Oct 30, 2016 at 5:18 AM Jay Abbott via swift-evolution <
swift-evolution at swift.org> wrote:

> @unwrappable(type: Int)
> public enum Count {
>     case none // not unwrappable
>     case many // not unwrappable
>     case some(Int)
>     case owed(Int)
>     case something(String) // not unwrappable
>     case multiple(Int, Int) // not unwrappable
> }
>
> Instead of requiring the @unwrappable attribute, why not have unwrap work
> normally when the type can be inferred, or require hints when it can’t:
>
> // For an optional (or any other enum with only one wrapped type)
> guard unwrap x else { return }// For an enum of type Count as defined above
> guard unwrap myCount else { return } // compiler error - type can't be determined
> guard unwrap(myCount: Int) else { return } // Success for 'some' or 'owed' (implicit shadowing)
> guard unwrap(let someOrOwed: Int) myCount else { return } // Success for 'some' or 'owed' (no shadowing)
> guard unwrap(let x: Int, let y: Int) myCount else { return } // Success for 'multiple' (no shadowing)
>
> Notes:
>
>    - unwrap x is equivalent to unwrap(x: T) where there is a single
>    unambiguous type.
>    - The let keyword probably could be implicit for the non-shadowing
>    forms, like it is for the shadowing form, but makes it clear what’s going
>    on.
>    - unwrap fails for none or many from the Count type, just as it does
>    for none from Optional
>    - I *think* that this assumes Swift is not allowed to try to infer the
>    most restrictive type for reference types. Haven’t really thought about
>    this much.
>
> ​
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20161030/6e167c40/attachment.html>