> On 22 Feb 2017, at 22:02, Slava Pestov via swift-users > <swift-users@swift.org> wrote: > > >> On Feb 22, 2017, at 1:01 PM, David Hart <david.w.h...@me.com >> <mailto:david.w.h...@me.com>> wrote: >> >> >>> On 22 Feb 2017, at 21:59, Slava Pestov via swift-users >>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >>> >>> When a class conforms to a protocol and a requirement is fulfilled by a >>> method in an extension, the class does not get a vtable entry for the >>> extension method. So it cannot be overridden in a subclass — there’s >>> nothing to dynamically dispatch here. We plan on addressing this as part of >>> ABI stability. >> >> What do you mean by “address” this? Force the vtable entry? > > Yeah. Instead of having the witness table for the conformance point directly > to the extension method, if the conforming type is a class, we will generate > a small thunk that calls a vtable entry, and store the extension method in > that vtable entry. > > Of course this will only work if the conformance is defined in the same > translation unit as the class; if you define the extension in a different > module, you’ll get the same behavior you observe below.
Sound great :) > Slava > >> >>> Slava >>> >>> >>>> On Feb 22, 2017, at 9:39 AM, David Hart via swift-users >>>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >>>> >>>> In the following piece of code, can somebody explain the last result? Why >>>> the break in consistency? Is this a bug? >>>> >>>> protocol P { >>>> func foo() -> String >>>> } >>>> >>>> extension P { >>>> func foo() -> String { return "P" } >>>> } >>>> >>>> class A : P { >>>> func foo() -> String { return "A" } >>>> } >>>> >>>> class B : P {} >>>> class C : B { >>>> func foo() -> String { return "C" } >>>> } >>>> >>>> A().foo() // A >>>> (A() as P).foo() // A >>>> B().foo() // P >>>> (B() as P).foo() // P >>>> C().foo() // C >>>> (C() as P).foo() // P >>>> _______________________________________________ >>>> 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> >>> >>> _______________________________________________ >>> 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> >> > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users
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