What type do I use for a Sequence of Strings
func doSomething<S: Sequence>(with seq: S) where S.Element == String
Or as per suggestion in comments by @LeoDabus you could include also substrings and other types conforming to StringProtocol by constraining the sequence’s element:
func doSomething<S: Sequence>(with seq: S) where S.Element: StringProtocol