[swift-users] Extensions on Typealiased Existential Protocols

[Steven Brunwasser]

Is this error intentional, or a bug?


protocol A {}


protocol B {}


typealias C = A & B // valid


extension C {} // Error: Non-nominal type 'C' (aka 'A & B') cannot be
extended


extension A where Self: B {} // valid


struct Foo: C {} // valid


Since extension A where Self: B is the same as extension B where Self: A,
and C is defined as any A that also inherits from B, shouldn’t extension C be
just as valid?

This seems like it should be valid, so I filed this bug,
https://bugs.swift.org/browse/SR-5260.

- Steve
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