[swift-evolution] [Proposal draft] Bridge Optional As Its Payload Or NSNull

[Omer Iqbal]

> The problem is that NSNull is in fact rare in Cocoa.

I couldn't agree more. I think this proposal is quite dangerous for (often
legacy) Objective C codebases where checking for NSNull is not common
practice. Since Optionals are not a construct in Objective C, I don't see
any reason for why Objective C Collection types would be populated with
Optionals unless it's unintentional.

I'm not sure whether it's possible, but an ideal solution would be if the
Swift Compiler can give a type error when passing an Optional to an
Objective C Collection type.

On Thu, Aug 25, 2016 at 9:27 AM, Greg Parker via swift-evolution <
swift-evolution at swift.org> wrote:

>
> On Aug 23, 2016, at 3:36 PM, Douglas Gregor via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Proposed solution
>
> When an Optional<T> value is bridged to an Objective-C object, if it
> contains some value, that value should be bridged; otherwise, NSNull or
> another sentinel object should be used.
>
> I don't think I like this.
>
> Let me verify my understanding. If I have this:
>
>     // imported from ObjC
>     func f(with object: Any)
>
>     let s: String? = nil
>     f(s)
>
> then at runtime it will call
>     f([NSNull null])
> ?
>
> The problem is that NSNull is in fact rare in Cocoa. They are used in the
> Foundation containers and almost nowhere else. Passing NSNull into almost
> any API is going to do something confusing at runtime. If you're lucky you
> get a prompt error "-[NSNull something]: unrecognized selector". If you're
> not lucky you'll get that error somewhere much later, or something even
> less obviously related to NSNull and your call site. That sounds like the
> wrong outcome for developers who are confused or careless or unaware of an
> optional.
>
>
> --
> Greg Parker     gparker at apple.com     Runtime Wrangler
>
>
>
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>
>
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