This sort of thing is a common pattern in Go, where it is accomplished by the fact that Go interfaces do not require types to opt into them by declaring their a

This sort of thing is a common pattern in Go, where it is accomplished by the fact that Go interfaces do not require types to opt into them by declaring their adoption. If a type conforms to the interface it's a type of the interface. So one can create a new interface type that supports the specific subset of functionality you need from a larger type that you don't control and use it in a similar way to Swift protocols.