Factory method inside interface

Support
2

The Kotlin way is to define a top-level constructor function for your interface with the same name as your interface:

fun Focusable(focusable: Focusable): Focusable {
    FocusableManager.list.add(focusable)
    return focusable
}

Although, a constructor function (or a function named create) with side effect is a very, very bad code smell.