Swift difference between uppercase "I" and lowercase "I"

Question

While playing on the Swift playground, I noticed that Self with capital "S" is available along with the lower case Self . Is there any difference between the two? If so, what are used for these two, especially for Self ?

Answer 1

Self refers to the type of current “thing” inside the protocol (which corresponds to the protocol). For an example of its use, see Function func returns Self .

The only official documents I have found for Self are in the Associated Protocol in Swift Programming. This is surprisingly not described in sections on protocols or nested types.

Answer 2

in the protocol and extension declaration use Self else self

 extension protocolName where Self: UIView { func someFunction() { self.layer.shadowColor = UIColor.red.cgColor } }