On Apr 10, 2017, at 9:53 AM, Kevin Nattinger <[email protected]<mailto:[email protected]>> wrote:
On Apr 10, 2017, at 9:18 AM, Josh Parmenter via swift-evolution <[email protected]<mailto:[email protected]>> wrote: case .none isn’t handled. It shouldn’t need to be handled in the second switch because it’s impossible. Not just developer thinks “impossible” but easily provable by static analysis the compiler is doing it anyway—I wouldn’t be surprised if including the case resulted in an “unreachable code” warning (in fact, it probably should). Why? Because of preconditionFailure? That COULD be optimized out as per this documentation: /// * In `-Ounchecked` builds, the optimizer may assume that this function is /// never called. Failure to satisfy that assumption is a serious /// programming error. So I’m not sure if that is the case or not. This should probably be on the swift-users list though, no? File a bug, IMO. Yes - it should probably be looked at by someone who would know if this a bug or the expected behavior. Best, Josh Best, Josh On Apr 8, 2017, at 11:29 AM, Drew Crawford via swift-evolution <[email protected]<mailto:[email protected]><mailto:[email protected]>> wrote: Is there a good reason we do not compile this: import UIKit func foo(operation: UINavigationControllerOperation) { switch(operation) { case .push: /* snip */ break case .pop: /* snip */ break default: preconditionFailure("This is a silly operation") } switch(operation) { case .push: /* snip */ break case .pop: /* snip */ break //error: Switch must be exhaustive, consider adding a default clause } } The switch *is* exhaustive, because the default case is unreachable. The compiler could infer as much from branch analysis. _______________________________________________ swift-evolution mailing list [email protected]<mailto:[email protected]><mailto:[email protected]> https://lists.swift.org/mailman/listinfo/swift-evolution Joshua Parmenter | Engineering Lead, Apple Technologies T 248 777 7777 C 206 437 1551 F 248 616 1980 www.vectorform.com<http://www.vectorform.com/><http://www.vectorform.com/> Vectorform 2107 Elliott Ave Suite 303 Seattle, WA 98121 USA Think Tank. Lab. Studio. We invent digital products and experiences. SEATTLE | DETROIT | NEW YORK | MUNICH | HYDERABAD _______________________________________________ swift-evolution mailing list [email protected]<mailto:[email protected]> https://lists.swift.org/mailman/listinfo/swift-evolution _______________________________________________ swift-evolution mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-evolution
