Access Control

Syntax#

private class Project
let car = Car(“Ford”, model: “Escape”) //default internal
public enum Genre
private func calculateMarketCap()
override internal func setupView()
private(set) var area = 0

Remarks#

Basic Remark:

Below are the three access levels from highest access (least-restrictive) to lowest access (most-restrictive)

Public access allows access to classes, structs, variables, etc from any file within the model, but more importantly outside the module if the external file imports the module containing the public access code. It is popular to use public access when you create a framework.

Internal access allows files only with the module of the entities to use the entities. All entities have internal acccess level by default (with a few exceptions).

Private access prevents the entity from being used outside of that file.

Subclassing Remark:

A subclass cannot have a higher access than its superclass.

Getter & Setter Remark:

If property’s setter is private the getter is internal (which is the default). Also you can assign access level for both the getter and the setter. These principles also apply to subscripts as well

General Remark:

Other entity types include: Initializers, Protocols, Extensions, Generics, and Type Aliases

Basic Example using a Struct

In Swift 3 there are multiple access-levels. This example uses them all except for open:

public struct Car {
    
    public let make: String
    let model: String //Optional keyword: will automatically be "internal"
    private let fullName: String
    fileprivate var otherName: String
    
    public init(_ make: String, model: String) {
        self.make = make
        self.model = model
        self.fullName = "\(make)\(model)"
        self.otherName = "\(model) - \(make)"
    }
}

Assume myCar was initialized like this:

let myCar = Car("Apple", model: "iCar")

Car.make (public)

print(myCar.make)

This print will work everywhere, including targets that import Car.

Car.model (internal)

print(myCar.model)

This will compile if the code is in the same target as Car.

Car.otherName (fileprivate)

print(myCar.otherName)

This will only work if the code is in the same file as Car.

Car.fullName (private)

print(myCar.fullName)

This won’t work in Swift 3. private properties can only be accessed within the same struct/class.

public struct Car {

    public let make: String       //public
    let model: String             //internal
    private let fullName: String! //private 

    public init(_ make: String, model model: String) {
        self.make = make
        self.model = model
        self.fullName = "\(make)\(model)"
    }
}

If the entity has multiple associated access levels, Swift looks for the lowest level of access. If a private variable exists in a public class, the variable will still be considered private.

Subclassing Example

public class SuperClass {
    private func secretMethod() {}
}
 
internal class SubClass: SuperClass {
    override internal func secretMethod() {
        super.secretMethod()
    }
}

Getters and Setters Example

struct Square {
    private(set) var area = 0

    var side: Int = 0 {
        didSet {
            area = side*side
        }
    }
}

public struct Square {
    public private(set) var area = 0
    public var side: Int = 0 {
        didSet {
            area = side*side
        }
    }
    public init() {}
}