[swift-users] Protocol extension gotcha... or bug?

[Zhao Xin]

Wagner, the `extension` of `protocol` is never dynamic. It is `fail safe`.
It means if you don't implement something, the compiler will use the
implementation in the `protocol extension`. As in swift, struct and enum
can also conform protocols.

If you want the other way, you should do it in a base class, not in a
protocol extension.

Zhaoxin

On Tue, Jan 24, 2017 at 4:32 AM, Wagner Truppel via swift-users <
swift-users at swift.org> wrote:

> On 23 Jan 2017, at 19:56, Slava Pestov <spestov at apple.com> wrote:
>
> class B: A {
>
>  var item: String { // subclass specialises 'item' by "overriding" the
> protocol extension implementation
>
>
> This is the problem. You’re not overriding the protocol extension version,
> you’re just shadowing it for the purposes of compile-time name lookup. Note
> that if you add the ‘override’ keyword here, the compiler complains because
> there’s nothing in the base class to override.
>
>
> Yes, that's why I wrote overriding in quotes and also why I tried to use
> the word specialise in place of override. My beef is not really here; this
> really was just a preamble. My issue is with the fact that adding the
> declaration to the protocol doesn't solve the problem despite the fact that
> the property is then supposed to be dynamically dispatched but isn't.
>
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>
>
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