A quick ping. I'd like some feedback about how to address this problem.
-Joe
> On Nov 2, 2016, at 10:26 AM, Joe Groff via swift-dev <swift-dev@swift.org>
> wrote:
>
> There's a hole in our AnyHashable implementation when it comes to what I'll
> call "pure" NSNumbers coming from Cocoa, which were instantiated using
> -[NSNumber numberWith*:] factories or @(n) syntax in Objective-C. While we
> maintain type specificity when Swift number types are bridged through
> NSNumber, NSNumbers constructed in ObjC do not necessarily remember the type
> they were constructed with or expect to be strictly used as only that type,
> so we resign to being "fuzzy" and let them bridge back to any Swift type. We
> however fail to bring this fuzziness to AnyHashable. When we construct an
> AnyHashable, we'll bring bridged NSNumbers back to their original Swift
> types, but we leave a pure NSNumber as an NSNumber, so it doesn't hash or
> equate with numeric values in Swift:
>
> // ObjC
> @import Foundation;
>
> NSDictionary *foo() {
> return @{@(1): @"one"};
> }
>
> // Swift
> let theFoo /*: [AnyHashable: Any]*/ = foo()
> theFoo[1] // returns nil, ought to find the value "one"
>
> One way to address this would be to make Swift's number types use the same
> hashing as NSNumber does. We could go so far as to switch the "custom
> AnyHashable" polarity around and coerce the Swift number types into NSNumbers
> when we put them inside AnyHashable, which would give us consistent hashing
> and fuzzy equality, but would come at a performance cost when converting a
> number to AnyHashable. We would also lose type specificity in equality for
> Swift values, since NSNumber's -isEqual: only compares numeric value, unless
> we special-cased NSNumber in AnyHashable's implementation.
>
> If we didn't want to adopt NSNumber's hashing for Swift's types, but we were
> willing to say that all of Swift's number types produce the same hashValue
> for the same numeric value (so 12.hashValue == 12.0.hashValue == (12 as
> UInt8).hashValue, etc.), we could also go the other direction, and customize
> a pure NSNumber's AnyHashable implementation to use Swift's number hashing.
> We would still need special handling for equality of a pure NSNumber with
> Swift numbers, but maybe that's inevitable.
>
> -Joe
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