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

[Sean Heber]

Putting “final” on a default method implementation that is inside of a protocol extension could maybe make some sense to prevent other implementations of that method, but final in the protocol itself doesn’t make sense to me.

l8r
Sean


> On May 18, 2016, at 2:18 PM, Leonardo Pessoa via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 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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>> 
>> 
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