Does Swift have access modifiers?

As of Swift 3.0.1, there are 4 levels of access, described below from the highest (least restrictive) to the lowest (most restrictive).


1. open and public

Enable an entity to be used outside the defining module (target). You typically use open or public access when specifying the public interface to a framework.

However, open access applies only to classes and class members, and it differs from public access as follows:

  • public classes and class members can only be subclassed and overridden within the defining module (target).
  • open classes and class members can be subclassed and overridden both within and outside the defining module (target).
// First.framework – A.swift

open class A {}

// First.framework – B.swift

public class B: A {} // ok

// Second.framework – C.swift

import First

internal class C: A {} // ok

// Second.framework – D.swift

import First

internal class D: B {} // error: B cannot be subclassed

2. internal

Enables an entity to be used within the defining module (target). You typically use internal access when defining an app’s or a framework’s internal structure.

// First.framework – A.swift

internal struct A {}

// First.framework – B.swift

A() // ok

// Second.framework – C.swift

import First

A() // error: A is unavailable

3. fileprivate

Restricts the use of an entity to its defining source file. You typically use fileprivate access to hide the implementation details of a specific piece of functionality when those details are used within an entire file.

// First.framework – A.swift

internal struct A {

    fileprivate static let x: Int

}

A.x // ok

// First.framework – B.swift

A.x // error: x is not available

4. private

Restricts the use of an entity to its enclosing declaration. You typically use private access to hide the implementation details of a specific piece of functionality when those details are used only within a single declaration.

// First.framework – A.swift

internal struct A {

    private static let x: Int

    internal static func doSomethingWithX() {
        x // ok
    }

}

A.x // error: x is unavailable

Leave a Comment