Sent from my iPad
> On May 25, 2016, at 12:04 PM, Leonardo Pessoa via swift-evolution > <[email protected]> wrote: > > I like the idea of sealed types but I think much better is Ceylon's concept > of previously declaring the many subclasses that are going to exist both > because I can have a bunch of public classes in a framework and restrict > their subclasses and because there are threads in this group discussing the > idea of a union type (perhaps both ideas could benefit from one another). I forgot to mention this in my last reply. What I am proposing allows sealed classes to be viewed as similar to nominal sum types. This is like Scala's case classes. Ceylon's unions are structural sum types (the sum type analogue of a Tuple, which is a structural product type). I really want to see these as well (I recently ran into a use case where they are far superior to what we can do today). But they are not the same as sealed classes and protocols. > > Another idea could be to add a single simple keyword to the root class (could > even be sealed but I don't think it grabs this concept) to declare all its > subclasses must exist within the same module. That would restrict the number > of subclasses to the compiler without requiring us to revisit the root class > each time we need to create a subclass and would still allow for every > subclass to be public. > > Sealed wouldn't be a good idea because the root class would still enable > subclassing and it would be ideal that the switch could only work with these > "sealed" types. > > +1 for enabling this for protocols too. > > Just a few issues: > - here we're considering having subclasses of subclasses, or not? > -what about public protocols being adopted outside the module, should we just > ignore them or completely forbid the adoption? > > From: Thorsten Seitz via swift-evolution > Sent: 25/05/2016 01:18 PM > To: Thorsten Seitz > Cc: swift-evolution > Subject: Re: [swift-evolution] [Pitch] Exhaustive pattern matching > forprotocols and classes > > Just realized that Matthew did introduce `sealed` exactly to enable this for > public types. That's fine with me! > > -Thorsten > >> Am 25.05.2016 um 18:11 schrieb Thorsten Seitz via swift-evolution >> <[email protected]>: >> >> Ceylon uses the following syntax for stating that a class has a finite set >> of subclasses: >> >> class C of C1 | C2 {...} >> >> where `|` is the type union operator. Swift could use a simple comma >> separated list instead after the `or`. The advantage over >> sealed+private/internal would be thatnthe class or protocol could be public >> as well. >> >> -Thorsten >> >>> Am 25.05.2016 um 04:01 schrieb David Sweeris via swift-evolution >>> <[email protected]>: >>> >>> 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 >>> _______________________________________________ >>> 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
_______________________________________________ swift-evolution mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-evolution
