[swift-evolution] [Draft] Abolish IUO type

[rintaro ishizaki]

Oops, typo in the example code:

let foo: Int! = 42
let bar = (foo as ImplicitlyUnwrappedOptional).map { UInt($0) }


2016-03-18 14:05 GMT+09:00 rintaro ishizaki <fs.output at gmail.com>:

> What will happen to map()/flatMap() on IUO attributed optional values?
>
> let foo: Int! = 42
> let bar = (foo as ImplicitlyUnwrappedOptional).map { $0.UInt($0) }
>
>
> Replacement would be something like this?
>
> let bar: UInt! = (foo as Int?).map { UInt($0) }
>
>
> I have never seen code like this in real world,
> but it should be covered in "Impact on existing code" section.
>
>
> 2016-03-18 13:12 GMT+09:00 Chris Lattner via swift-evolution <
> swift-evolution at swift.org>:
>
>>
>> > On Mar 17, 2016, at 9:08 PM, Chris Lattner via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> >
>> > On Mar 17, 2016, at 5:50 PM, Brent Royal-Gordon <brent at architechies.com>
>> wrote:
>> >
>> >>> It seems like this unnecessarily complicates the surface model of
>> Swift.  To me, it seems like there is no advantage to having two ways to
>> spell this.
>> >>
>> >>   @autounwrapped let foo = functionReturningOptional()
>> >>
>> >> I *believe* that, without the `@autounwrapped` attribute, there's no
>> way to go from T? to T! without actually restating T somewhere.
>> >
>> > Right, that's part of the feature :-)
>>
>> Sorry, less snarky answer:
>>
>> You are right that today it is a regression vs:
>>
>> let foo : ImplicitlyUnwrappedOptional = ...
>>
>> However, I have never seen someone actually do that, and if they did, I
>> would observe that the T is a lot more illuminating than the ! part of the
>> type.  Is there a concrete use case you are concerned about?
>>
>> -Chris
>>
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>>
>
>
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