Still a bit confused on what opaque types are, but this video is a short and sweet explanation into them. Basically, when compared to a protocol (the most similar language feature), here are the differences:
- Protocol returns any sort of a thing and we don’t know what (other than the protocol type).
- Opaque type returns a specific sort of thing but we still don’t know what.
So for example, Equatable protocol we would define the underlying type that conforms to the protocol (e.g. a string) when we call it. Or, if it’s just an Equatable we have no idea it’s a string.
With some Equatable we don’t need to define the underlying type when we call it. It can just be some equatable. And we can compare that with some other equatable (compiler knows the underlying type is a string for instance).
Other things to know:
- Hides implementation details (can swap out what’s underneath in the future).
- Can only return one specific type.
- Anytime you see
someit means opaque type. - Introduced in Swift 5.1 (common in SwiftUI with
some View.