I'm pretty sure solutions like the one you proposed are impossible,
unfortunately :(. The compiler has to choose the static override at compile
time, but it can't tell until runtime whether the type conforms to `Equatable`
or not (because of retroactive conformance).
It's also not possible to use the as or is dynamic casting machinery to work
with `Equatable`, because of the use of the `Self` type in its requirements.
A feature that the community has expressed interest in, "generalized
existentials", may allow you to implement a function that does what you want.
Best,
Austin
> On Jul 3, 2017, at 5:00 PM, David Baraff via swift-users
> <swift-users@swift.org> wrote:
>
> I’m searching for the simplest way to write a function
> func maybeEqual<T>(_ lhs:T, _rhs:T) -> Bool
>
> where it returns lhs == rhs if T is equatable, and false, otherwise.
> I tried
>
> func maybeEqual<T>(_ lhs:T, _rhs:T) -> Bool {
> return false
> }
>
> func maybeEqual<T:Equatable>(_ lhs:T, _ rhs:T) -> Bool {
> return lhs == rhs
> }
>
> but that doesn’t work. Is there a way to express a type not matching
> something?
> Alternately, how can I write this?
>
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