Swift Access Control

Swift Access Control

Restrict visibility of types and members with public, internal, fileprivate, and private.

Levels

Swift's defaults are safe by design: internal is the default.

Syntax:

• public (visible to other modules)
• internal (module-only, default)
• fileprivate (this file)
• private (this scope type/extension)

public struct APIClient {
  public init() {}
  public func request() {}
}

struct Repository { // internal by default
  fileprivate var cache: [String: String] = [:]
  private func reset() { cache.removeAll() }
}

This example shows public APIs, a module-internal type, a file-scoped property, and a private helper.

Types and Members

A member cannot be more visible than its enclosing type.

Syntax:

• public struct S { internal var x: Int } (valid)
• but not internal struct S { public var x: Int }

internal struct Box { // whole type is internal
  public var value: Int // warning/error: member more visible than type
}

Members cannot exceed the visibility of their type; lower or equal visibility is allowed.