[swift-evolution] [Proposal] [Discussion] Explicit Toll-Free Conversions

Joe Groff jgroff at apple.com
Thu Mar 23 11:05:52 CDT 2017

> On Mar 22, 2017, at 10:41 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
>> On Mar 22, 2017, at 10:35 PM, Robert Widmann via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Alternatives considered
>> Do nothing and continue to accept this implicit conversion.
> One alternative would be to import CFArray as a typealias for NSArray, etc, erasing the distinction between the two types completely. I did suggest this to Jordan at one point and he pointed out some problems, but I don’t remember them now. Hopefully Jordan can chime in.

I'd prefer this solution as well, especially since toll-free bridged CF types are nearly indistinguishable from their NS counterparts at runtime, so trying to maintain the distinction for dynamic casts or reflection has historically been problematic. Part of the problem is that, as Charlie noted, CFArray/Dictionary/Set can take an arbitrary set of retain/release callbacks, in which case the resulting container isn't fully NSArray-compatible. I'm not sure that happens often enough with CF containers in the SDKs that accounting for that case is worth the burden of separating the types.

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