Xcode 8 and 9
iOS cocoa frameworks
I couldn't figure out a pure-Swift use case, but Apple's Cocoa framework seems to expose an issue with the compiler in regards to how values are cast within a case comparison.
In these example case comparisons, kUTTypeImage is of type CFString.
I'd expect this line to work, but the compiler flags with the error, "‘CFString’ is not implicitly convertible to ‘String’; did you mean to use ‘as’ to explicitly convert?"
This line works, but it seems wrong to have to cast twice.