What is a good example to differentiate between fileprivate and private in Swift3

Question

This article has been helpful in understanding the new access specifiers in Swift 3. It also gives some examples of different usages of fileprivate

Answer 1

class Privacy {

    fileprivate(set) var pu:Int {
        get {
            return self.pr
        }
        set {
            self.pr = newValue
        }
    }
    private var pr:Int = 0
    fileprivate var fp:Int = 0


    func ex() {
        print("\(self.pu) == \(self.pr) and not \(self.fp)")
    }
}


extension Privacy {

    func ex2() {
        self.pu = 5
        self.ex()
    }

}

I like this because it is super simple for ivars.

Try changing fileprivate to private (and vice versa) and see what happens on compile...

Answer 2

Although @MartinR's and @StephenChen's answer are perfect, Swift 4 changes things a little bit.

Private is now considered as private to a class in which it is declared and also to its extensions.

FilePrivate is considered to be private in that file be it a class in which the variable is defined, it's extension, or any other classes defined in that same file.

Answer 3

A practical rule of thumb is that you use private for variables, constants, inner structs and classes that are used only inside the declaration of your class / struct. You use fileprivate for things that are used inside of your extensions within the same file as your class/struct but outside of their defining curly braces (ie. their lexical scope).

    class ViewController: UIViewController {
        @IBOutlet var tableView: UITableView!
        //This is not used outside of class Viewcontroller
        private var titleText = "Demo"
        //This gets used in the extension
        fileprivate var list = [String]()
        override func viewDidLoad() {
            navigationItem.title = titleText
        }
    }

    extension ViewController: UITableViewDataSource {
        func numberOfSections(in tableView: UITableView) -> Int {
            return list.count
        }
    }

Answer 4

filePrivate - access controll level is within the file.

case 1: If we create extension with in same class file and try to access fileprivate function or fileprivate property in its extension - access allowed
case 2: If we create a extension of class in new file - And now try to access fileprivate function or fileprivate property - access not allowed

private - access control level is with in lexical scope

case 1: If property or function is declared as private in class - then scope is by default the class. case 2: if private instance is declared with in function body - then scope of instance is limited to function body.