UserDefaultsKey-Example.swift

import Foundation

// MARK: - Library

public extension UserDefaults {
	struct Key<Value> {
		let key: String

		public init(key: String) {
			self.key = key
		}
		public init(key: String, value _: Value.Type) {
			self.init(key: key)
		}
	}

	struct DefaultValueKey<Value> {
		let key: String
		let defaultValue: () -> Value

		public init(key: String, defaultValue: @escaping @autoclosure () -> Value) {
			self.key = key
			self.defaultValue = defaultValue
		}
	}
}

#if canImport(SwiftUI)
import SwiftUI

@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
public extension AppStorage where Value == String {
	init(wrappedValue: Value, _ key: UserDefaults.Key<Value>) {
		self.init(wrappedValue: wrappedValue, key.key)
	}

	init(_ key: UserDefaults.DefaultValueKey<Value>) {
		self.init(wrappedValue: key.defaultValue(), key.key)
	}
}
#endif

public extension UserDefaults {
	func removeObject<Value>(for key: Key<Value>) {
		removeObject(forKey: key.key)
	}

	func removeObject<Value>(for key: DefaultValueKey<Value>) {
		removeObject(forKey: key.key)
	}

	func setValue<Value>(_ value: Value, for key: Key<Value>) {
		setValue(value, forKey: key.key)
	}

	func setValue<Value>(_ value: Value, for key: DefaultValueKey<Value>) {
		setValue(value, forKey: key.key)
	}

	func string(for key: Key<String>) -> String? {
		string(forKey: key.key)
	}

	func string(for key: DefaultValueKey<String>) -> String {
		register(defaults: [key.key: key.defaultValue()])
		return string(forKey: key.key) ?? key.defaultValue()
	}
}




// MARK: - Example of App Code
extension UserDefaults.Key where Value == String {
	static let username = Self(key: "username")
}

extension UserDefaults.DefaultValueKey where Value == String {
	static let autoPlay = Self(key: "autoPlay", defaultValue: "Hiho")
}

UserDefaults.standard.string(for: .autoPlay)

struct V: View {
	@AppStorage(.autoPlay) var autoPlay
	var body: some View { Text("") }
}