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

[Adrian Zubarev]

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  
    }
}


— 
Regards Adrian
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