How would you check equality between a compile-time protocol reference and a conformance?

[NSExceptional]

i.e. you want to check if Equatable.self is present in metadata.conformances. Can't seem to wrap my head around how to compare the two besides comparing the names which is not intuitively reliable

[Azoy]

So doing something like reflect(Equatable.self) isn't possible yet (soon it will be because of https://forums.swift.org/t/se-0309-unlock-existential-types-for-all-protocols/47515 !), but if one really wants to do this kind of operation now you could do something pretty hacky.

let equatableMetadata = reflect(_typeByName("SQ")!) as! ExistentialMetadata
let equatable = equatableMetadata.protocols[0]

for conformance in metadata.conformances {
  if conformance.protocol == equatable { /* ... */ }
}

I'm thinking I may want to make the conformances a dictionary with the protocol as the key instead. Keep in mind that ExistentialMetadata is not ABI stable so it can change in the future, but for experimenting purposes this works right now.

[NSExceptional]

Ugh, of course that was conveniently left out when we got ABI stability ;(

Thanks!

Edit: for anyone reading this, to make it work with SomeProtocol.self, you need to do this:

extension TypeMetadata {
    func conforms(to _protocol: Any) -> Bool {
        let metatype = reflect(_protocol) as! MetatypeMetadata
        let existential = metatype.instanceMetadata as! ExistentialMetadata
        let desc = existential.protocols.first!

        return !conformances.filter({ $0.protocol == desc }).isEmpty
    }
}

let conforms = someTypeMetadata.conforms(to: SomeProtocol.self)

[NSExceptional]

Do you think this sort of check is something you would want to provide in Echo itself? Or at a higher level in another library instead?