Distinction in Swift between uppercase “Self” and lowercase “self”

Question

While playing in a Swift playground I noticed that Self, with capital \"S\", is available along with the lowercase self. Is there any difference be

Answer 1

I think this question could use a simpler answer, more focussed on the difference between Self and self, and perhaps aimed at people newer to Swift.

self - explicit reference to the current type or instance of the type in which it occurs.

class MyClass {
  func showClass() {
       print("\(self)")
    }
  }
let someClass = MyClass()
someClass.showClass()
// prints "MyClass"

Self - Used specifically in protocol and extension declarations to refer to the eventual type that will conform to the protocol.

protocol MyProtocol {
   static func returnSelf() -> Self
}

class MyClass: MyProtocol {
   // define class
}

MyClass.returnSelf() 
// returns MyClass

The difference is that self is used in types and instances of types to refer to the type that it's in; and Self is used in protocols and extensions where the actual type is not yet known.

In even simpler terms, self is used within an existing type; Self is used to refer to a type that Self is not yet in.

Read more here:

• Self - https://docs.swift.org/swift-book/ReferenceManual/Declarations.html#//apple_ref/doc/uid/TP40014097-CH34-XID_543
• self - https://docs.swift.org/swift-book/ReferenceManual/Expressions.html
• Both - https://medium.com/the-traveled-ios-developers-guide/swift-keywords-v-3-0-1-f59783bf26c