> On Feb 5, 2017, at 7:45 AM, Karl Wagner <razie...@gmail.com> wrote:
>
> I have a question about current dispatching behaviour with protocols and
> ‘Self’.
>
> protocol CustomEquatable {
> func equal(to: Self) -> Bool
> }
>
> open class Super : CustomEquatable {
> func equal(to: Super) -> Bool { print("super"); return false }
> }
> class Sub: Super {
> func equal(to: Sub) -> Bool { print("sub-sub"); return true }
> override func equal(to: Super) -> Bool { print("sub-super"); return true }
> }
>
> Sub().equal(to: Sub()) // sub-sub
> Sub().equal(to: Super()) // sub-super
> Super().equal(to: Sub()) // super
> Super().equal(to: Super()) // super
>
> (Sub() as Super).equal(to: Sub) // sub-super — dynamically
> dispatched to callee’s type, not param
> (Sub() as Super).equal(to: (Sub() as Super)) // sub-super — as above
>
>
> Currently, we dynamically dispatch to the callee’s type to find ‘Self’, but
> we don’t apply that consistently when dispatching to ‘Self’-type parameters.
> Is that expected behaviour?
>
> - Karl
Hi Karl,
This is expected behavior. The choice of method overload is based on the static
types: `Super.equal(to: Super)`. The dynamic dispatch that you get when using
the override keyword is based on the `self` argument’s dynamic type only. The
dynamic types of the non-self arguments don’t play a part.
I’m sure there are some good language design reasons not to support dynamic
method overloads. I can only tell you that implementing it would be no fun.
-Andy
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