Or if there was a way to declare that a class/protocol can only have a defined set of subclasses/conforming types.
Sent from my iPhone > On May 24, 2016, at 15:35, Austin Zheng via swift-evolution > <[email protected]> wrote: > > If you pattern match on a type that is declared internal or private, it is > impossible for the compiler to not have an exhaustive list of subclasses that > it can check against. > > Austin > >> On Tue, May 24, 2016 at 1:29 PM, Leonardo Pessoa <[email protected]> wrote: >> I like this but I think it would be a lot hard to ensure you have all >> subclasses covered. Think of frameworks that could provide many >> unsealed classes. You could also have an object that would have to >> handle a large subtree (NSObject?) and the order in which the cases >> are evaluated would matter just as in exception handling in languages >> such as Java (or require some evaluation from the compiler to raise >> warnings). I'm +1 for this but these should be open-ended like strings >> and require the default case. >> >> On 24 May 2016 at 17:08, Austin Zheng via swift-evolution >> <[email protected]> wrote: >> > I have been hoping for the exhaustive pattern matching feature for a while >> > now, and would love to see a proposal. >> > >> > Austin >> > >> > On Tue, May 24, 2016 at 1:01 PM, Matthew Johnson via swift-evolution >> > <[email protected]> wrote: >> >> >> >> Swift currently requires a default pattern matching clause when you switch >> >> on an existential or a non-final class even if the protocol or class is >> >> non-public and all cases are covered. It would be really nice if the >> >> default clause were not necessary in this case. The compiler has the >> >> necessary information to prove exhaustiveness. >> >> >> >> Related to this is the idea of introducing something like a `sealed` >> >> modifier that could be applied to public protocols and classes. The >> >> protocol or class would be visible when the module is imported, but >> >> conformances or subclasses outside the declaring module would be >> >> prohibited. >> >> Internal and private protocols and classes would implicitly be sealed >> >> since >> >> they are not visible outside the module. Any protocols that inherit from >> >> a >> >> sealed protocol or classes that inherit from a sealed class would also be >> >> implicitly sealed (if we didn’t do this the sealing of the superprotocol / >> >> superclass could be violated by conforming to or inheriting from a >> >> subprotocol / subclass). >> >> >> >> Here are examples that I would like to see be valid: >> >> >> >> protocol P {} >> >> // alternatively public sealed protocol P {} >> >> struct P1: P {} >> >> struct P2: P {} >> >> >> >> func p(p: P) -> Int { >> >> switch p { >> >> case is P1: return 1 // alternatively an `as` cast >> >> case is P2: return 2 // alternatively an `as` cast >> >> } >> >> } >> >> >> >> class C {} >> >> // alternatively public sealed class C {} >> >> class C1: C {} >> >> class C2: C {} >> >> >> >> func c(c: C) -> Int { >> >> switch c { >> >> case is C1: return 1 // alternatively an `as` cast >> >> case is C2: return 2 // alternatively an `as` cast >> >> case is C: return 0 // alternatively an `as` cast >> >> } >> >> } >> >> >> >> I am wondering if this is something the community is interested in. If >> >> so, I am wondering if this is something that might be possible in the >> >> Swift >> >> 3 timeframe (maybe just for private and internal protocols and classes) or >> >> if it should wait for Swift 4 (this is likely the case). >> >> >> >> -Matthew >> >> _______________________________________________ >> >> swift-evolution mailing list >> >> [email protected] >> >> https://lists.swift.org/mailman/listinfo/swift-evolution >> > >> > >> > >> > _______________________________________________ >> > swift-evolution mailing list >> > [email protected] >> > https://lists.swift.org/mailman/listinfo/swift-evolution >> > > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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