[swift-evolution] Abstract methods

[Trevör Anne Denise]

> to me protocol extensions are both cool and evil. cool as you can add code.
> evil because it's more natural to add another declarations in those
> extensions rather than implementation:
> 
> protocol Foo {
>    func foo()
> }
> 
> extension Foo {
>   func bar()    //*** natural assumption is that i can do this. but i can't
> }

While this can indeed be a common mistake, it feels much less natural to do that once you think about what protocol conformances mean and what it would take to make it possible IMO.