[swift-evolution] Proposal: Finalization in protocol extensions and default implementations

[Leonardo Pessoa]

Adrian, what would be the meaning of this final declaration? In my
understanding, a final means there can be no more overrides of that
method but there are no implementations in a protocol so I really
don't understand this use.

On 18 May 2016 at 16:15, Matthew Johnson via swift-evolution
<swift-evolution at swift.org> wrote:
>
> On May 18, 2016, at 12:53 PM, Adrian Zubarev via swift-evolution
> <swift-evolution at swift.org> wrote:
>
> I’d like to revive this idea I posted long time ago. There is only one thing
> I need to update here:
>
> protocol MagicType: class /* missed the class constraint */ {
>
>     final var foo: Int { get }
>     final func boo()
> }
>
> What benefit is there in defining a protocol requirement as final?
>
> What do you guys think? Is there any technical reason why this is not
> possible?
>
> --
> Adrian Zubarev
> Sent with Airmail
>
> Am 5. Dezember 2015 bei 16:26:23, Adrian Zubarev
> (adrian.zubarev at devandartist.com) schrieb:
>
> Hello there,
>
> I wonder if it is a good idea to be able to finalize in protocols and
> default implementations.
>
> Here is an example:
>
> protocol MagicType {
>
>     final var foo: Int { get }
>     final func boo()
> }
>
> class X: MagicType {
>
>     final var foo: Int {
>
>         return 42
>     }
>
>     final func boo() {
>
>         print("magic")
>     }
> }
>
> class Y: X {
>
>     // can't override func boo or var foo in here
> }
>
> //===================================================//
>
> protocol SomeType {}
>
> extension SomeType {
>
>     final func foo() {
>
>         print("Hello World")
>     }
> }
>
> class A: SomeType {}
>
> class B: SomeType {
>
>     /* this should raise an error, because the class B shouldn't */
>     /* be able to override that function from SomeType */
>
>     func foo() {
>         // do something else
>     }
> }
>
> How do you anticipate this would interact with retroactive modeling of types
> which would conform the requirements of `SomeType` but also happen to have a
> `foo` method?
>
>
>
> —
> Regards Adrian
>
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