Swift Classes Initialization Import - ?

Question

iOS

Comrades, explain to an incomprehensible person in an intelligible language.
1) It is not necessary to import classes in Swift3, are they added themselves?
2) Why does this not work:
file test.swift

class Dog {
    func bark() {
        print("woof") // This is a comment
    }
}

ViewController.swift file

class ViewController: UIViewController {
    
 
    let kit = Dog()
    kit.bark()
    

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }
}

Answer 1

I have not dealt with Swift yet, but it seems to me that

let kit = Dog()
    kit.bark()

you need to put in func viewDidLoad ()
and of course initialize the ViewController itself

Answer 2

Within the application code, classes do not need to be imported, because they are all considered inside the same module, so they see each other, but if you add another application to yours, then you already need to do import.