I have a general function that it is not in any class. Is it possible for that function call to a method that is inside a class?

Simplified here:

func func1() {
    //do something and then:
    //func2()
}

class ViewController: NSViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

    }

    func func2() {
        print ("content of func 2")
    }
}

If:

1. you have a reference to a specific instance of that class, or
2. the function you are calling is a class function.

import Foundation

class ThingClass {
    func doSomething() {
        print("do do do")
    }

    class func doSomethingElse() {
        print("hello!")
    }
}

func callFunction(on thing: ThingClass) {
    thing.doSomething()
}

func callClassFunction() {
    ThingClass.doSomethingElse()
}

let thing = ThingClass()
callFunction(on: thing)

callClassFunction()