Postfix Self Expression
A postfix self expression consists of an expression or the name of a type, immediately followed by .self. It has the following forms:
-
expression.self -
type.self
The first form evaluates to the value of the expression. For example, x.self evaluates to x.
The second form evaluates to the value of the type. Use this form to access a type as a value. For example, because SomeClass.self evaluates to the SomeClass type itself, you can pass it to a function or method that accepts a type-level argument.
GRAMMAR OF A SELF EXPRESSION
postfix-self-expression → postfix-expression.self
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-self-expression