Can a Swift Property Wrapper reference the owner of the property its wrapping?

Question

From within a property wrapper in Swift, can you someone refer back to the instance of the class or struck that owns the property being wrapped? Using self doesn\'t

Answer 1

The answer is yes! See this answer

Example code for calling ObservableObject publisher with a UserDefaults wrapper:

import Combine
import Foundation

class LocalSettings: ObservableObject {
  static var shared = LocalSettings()

  @Setting(key: "TabSelection")
  var tabSelection: Int = 0
}

@propertyWrapper
struct Setting {
  private let key: String
  private let defaultValue: T

  init(wrappedValue value: T, key: String) {
    self.key = key
    self.defaultValue = value
  }

  var wrappedValue: T {
    get {
      UserDefaults.standard.object(forKey: key) as? T ?? defaultValue
    }
    set {
      UserDefaults.standard.set(newValue, forKey: key)
    }
  }

  public static subscript(
    _enclosingInstance object: EnclosingSelf,
    wrapped wrappedKeyPath: ReferenceWritableKeyPath,
    storage storageKeyPath: ReferenceWritableKeyPath>
  ) -> T {
    get {
      return object[keyPath: storageKeyPath].wrappedValue
    }
    set {
      (object.objectWillChange as? ObservableObjectPublisher)?.send()
      UserDefaults.standard.set(newValue, forKey: object[keyPath: storageKeyPath].key)
    }
  }
}