[swift-evolution] [Pitch] Bridging nil to Objective-C Primitives

[Charles Srstka]

> On Feb 13, 2017, at 9:33 PM, Jeff Kelley via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hi all,
> 
> 	I don’t have a formal proposal written up yet, but in my continued quest to make better-annotated Objective-C code, I had an idea for bridging nil with primitives. Since in Objective-C we often use constant values to represent invalid values or nil, the most obvious being NSNotFound, could we use that as a shorthand for nil? Something like this for NSArray:
> 
> - (NSUInteger NS_SWIFT_NIL(NSNotFound))indexOfObject:(ObjectType)anObject;
> 
> 	This is a little verbose, so it could also work with a typedef:
> 
> typedef NSUInteger NS_SWIFT_NIL(NSNotFound) NSArrayIndex;
> - (NSArrayIndex)indexOfObject:(ObjectType)anObject;
> 
> 	This would change the existing Swift interface to return an Int? instead of an Int. I see this as working both ways—converting these values to nil when returning from Objective-C to Swift, and sending these values instead of nil when Swift calls into Objective-C code.
> 
> 	Is this worth writing up a proposal for? Is another, better method already in someone’s mind?

What happens if code on the Swift side sets the property’s value to the sentinel?

Charles

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