You can see in the image below that I was trying to extend the Collection protocol to include a method called removingDuplicates, which is supposed to do exactly what it says. The error that the compiler is displaying seems to directly contradict the definition of the Equatable protocol. Is this a bug or am I misunderstanding something?
The == function (all operators are actually functions in Swift) is a requirement of the Equatable protocol, which means it must be used with some concrete implementations of the protocol.
Another aspect is that Collection is a generic type, and its Element associated type will need to eventually be also filled with a concrete type, and == Equatable doesn't help here.
Actually it's not even possible to have a collection of generic Equatable values, as Equatable is a protocol with Self requirements, thus it can be directly referenced in a lot of places, e.g. [Equatable], one reason being the fact that that declaration can't satisfy the "collections are homogenous" requirement as you'd be able ot place two completely unrelated types in the array that way.
What you need to do is to transform the equality where clause to a conformance one: extension Collection where Element: Equatable. This moves the burden of providing an actual implementation on the user of the extension. And allows you to use the support brought by the Equatable type.
