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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