Thanks for your comment. But I disagree with you. Typealias is useful when it shortens some specific complex and long definitions. It makes code readable. But it is not a type and, it does not define any scope.

If you define a function as you mentioned, I can call the function from any string instance and from anywhere. It causes the function to become context-free.

Writing utility class for email validation groups validation related functions very well. Yes, I wrote the example, I know. But, it is wrong in terms of classification. Kotlin is a Type-Safe language. Thus we should take advantage of type definitions. I suggest you take a look at the "Primitive Obsession" topic.