class in playground vs in program file

I have a question about something simple that works in Playground but not in a Project: (Playground code below)

In the project where the class is in a separate swift file the code correction won't show me the the person.lastName and if I fully type it give me an error.... hmm, very strange - might be a beginner error or?

How would I have to state in in the program file and the separate swift file to work?

Thanks, Roman

import UIKit

class human {
    var firstName = ""
    var lastName = ""
}

let person = human()

person.lastName = "Smith"
person.firstName = "Peter"

print (person.firstName)
print (person.lastName)

This is why I hate playgrounds. They are not really Swift. In real Swift, all executable code must be inside a function (e.g. a method of some class or struct or enum); you can't have lines like person.lastName = "Smith" just hanging in space like that.

So in a real iOS project you'd need to write something more like this:

class Human {
    var firstName = ""
    var lastName = ""
}

func test() {

    let person = Human()

    person.lastName = "Smith"
    person.firstName = "Peter"

    print (person.firstName)
    print (person.lastName)

}

And even then nothing would happen until you actually call test(), and you can't do that except in a function. This is why people usually test code in the viewDidLoad of a view controller.

class Human {
    var firstName = ""
    var lastName = ""
}
class ViewController : UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let person = Human()

        person.lastName = "Smith"
        person.firstName = "Peter"

        print (person.firstName)
        print (person.lastName)

    }
}