Hi Mario, You’re right that this part of the proposal was not fully implemented. Computing the common ancestor of two superclasses is a little tricky here because it would force us to resolve the superclass type of a class when realizing a subclass existential. This would introduce circular dependencies. Either I missed something obvious or it would require some re-architecting of the type checker to make it work.
Either way, yes it’s a known limitation, but not one that is tracked by a JIRA presently, so please do file a bug! Thanks, Slava > On Dec 7, 2017, at 7:17 AM, Mario Meili via swift-users > <swift-users@swift.org> wrote: > > Hi everyone, > > I noticed strange behaviour of the Swift 4.0.3 compiler regarding class and > subtype existentials. > > According to the proposal SE-0156 > (https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md > > <https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md>), > multiple class types in protocol compositions should be allowed, if: > > The class types are the same > Or, one class type must be a subtype of the other. > > However, when copying the exact code from the proposal into Xcode 9.2, the > result is the following: > > <image001.png> > > My conclusion here is that the compiler does not allow multiple class types > in one protocol composition. > > My question is: > Is this behaviour intended or should I open a bug report? > > Thank you very much > > BR > Mario > _______________________________________________ > swift-users mailing list > swift-users@swift.org <mailto:swift-users@swift.org> > https://lists.swift.org/mailman/listinfo/swift-users > <https://lists.swift.org/mailman/listinfo/swift-users>
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