[swift-evolution] Pitch: Automatically deriving Equatable/Hashable for more value types

[Nevin Brackett-Rozinsky]

On Fri, May 5, 2017 at 1:47 AM, Xiaodi Wu via swift-evolution <
swift-evolution at swift.org> wrote:

> On Fri, May 5, 2017 at 12:41 AM, Brent Royal-Gordon <
> brent at architechies.com> wrote:
>
>> I would think only final classes could participate in this, since a
>> subclassable class would need to allow subclasses to override equality, and
>> you can't override a static `==` operator method.
>>
>
> I work so rarely with classes that I'm embarrassed to have to ask this
> question: can classes not satisfy Equatable with a `public class func ==`?
>

Currently:

class C: Equatable {
    class func == (lhs: C, rhs: C) -> Bool {
        return lhs === rhs
    }
}

Yields an error, “Operator '==' declared in non-final class 'C' must be
'final'”.

Nevin
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