Just one question: If I have functions
json_encode(j: JSON) -> String
and
json_decode(j: String) -> JSON throws
what should be the type of JSON? What should '{"a":2,"b":null}' decode to? What
should the type of the JSON null value be in Swift? I think String and String?
and String??? are wrong in this case.
I'm not saying that I'm convinced that NSNull() is the best way to represent
null in this case. I just want to explain the use case that I was thinking of.
-Michael
> Am 26.06.2016 um 19:53 schrieb David Rönnqvist via swift-evolution
> <[email protected]>:
>
> I'm not convinced that Swift needs more than on way of representing the lack
> of a value. As far as I've understood (and remember), NSNull main reason to
> exist is that it's an actual object and won't for example terminate array
> literals. From what I've observed of people who are new to Objective-C,
> NSNull is a big surprise, both its general existence but also when to expect
> it (read check for NSNull to make sure one doesn't crash) and when not to.
>
> The way I've imagined that the same problem would be solved in Swift is with
> an optional, optional value. That is: if a field in a response can either be
> set or not, that's an optional. If that field can either contain a value or
> the explicit lack of a value that's another optional:
>
> let nickname: String?? = "Little Bobby Tables"
>
> As I see it, this is both safer (requiring that the inner nil value is dealt
> with), serves as a documentation of when an explicit missing value is
> expected and when it's not, and is more consistent.
>
> I would still expect a newcomer to wonder why there is two question marks in
> some places, but I'd imagine that that explanation would feel more logical.
>
> And it's (still) possible (at least in the latest Swift Playground) to safely
> unwrap both levels:
>
> if case let name?? = nickname { }
>
> - David
>
> Sent from my iPad
>
> On 24 Jun 2016, at 11:32, Brent Royal-Gordon via swift-evolution
> <[email protected]> wrote:
>
>>> Not really. What is the type of Optional.none? `let empty = Optional.none`
>>> does not compile, it says "Generic parameter 'Wrapped' could not be
>>> inferred". NSNull() is a unique concrete value, and it's compatible with
>>> Objective C, NSObject and AnyObject. We could of course use
>>> `Optional<Int16>.none`, but someone else may use `Optional<AnyObject>.none`
>>> instead. The extra type information is just misleading in this case.
>>
>> If you want a single, unique value, use `()`.
>>
>> But I'm not sure why you wouldn't just make this member an Optional<Any> in
>> the first place. Is there some reason that wouldn't be suitable?
>>
>> --
>> Brent Royal-Gordon
>> Architechies
>>
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