[swift-evolution] [Review] SE-0140: Bridge Optional As Its Payload Or NSNull

[Charles Srstka]

> On Sep 6, 2016, at 7:11 PM, Douglas Gregor <dgregor at apple.com> wrote:
> 
> I *think* Charles is saying something slightly different here, and it’s a viewpoint I hadn’t considered before.
> 
> We agree that there should be some kind of diagnostic when putting an optional into an Any, because it’s probably not what the user intended. And we know it can happen in ways we cannot diagnose statically, so the diagnostic won’t be perfect. I think Charles is saying that, when this happens, we don’t *want* our Objective-C code to be able to query the value in that optional: in other words, it’s effectively a programmer error to treat such objects as anything more than completely-opaque objects that get passed around any perhaps dealt with properly in Swift code itself.

I’d say my position has three planks on it, and the above is pretty much the first plank: 1) the idea of an array of optionals is a concept that doesn’t really exist in Objective-C, and I do think that passing one to Obj-C ought to be considered a programmer error.

The other two planks would be:

2) Bridging arrays of optionals in this manner could mask the aforementioned programmer error, resulting in unexpected, hard-to-reproduce crashes when an NSNull is accessed as if it were something else, and:

3) Objective-C APIs that accept NSNull objects are fairly rare, so the proposed bridging doesn’t really solve a significant problem (and in the cases where it does, using a map to replace nils with NSNulls is not difficult to write).

Charles

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