Property Wrapper

PropertyWrapper.swift

import Foundation

/// A property wrapper that provides type-safe access to user defaults.
@propertyWrapper
struct UserDefault<Value> {
    // MARK: Properties
    
    /// The wrapped value representing the user default.
    var wrappedValue: Value {
        get {
            // Try to get the value for the provided key from UserDefaults.
            // If the value is not found or the types don't match, return the default value.
            UserDefaults.standard.object(forKey: self.key) as? Value ?? self.defaultValue
        }
        set {
            // Set the value for the provided key in UserDefaults.
            UserDefaults.standard.setValue(newValue, forKey: self.key)
        }
    }
    
    /// The key used to identify the user default in UserDefaults.
    let key: String
    
    /// The default value to use when the user default is not set.
    let defaultValue: Value
    
    // MARK: Initialization
    
    /// Creates a UserDefault property wrapper with the specified key and default value.
    /// - Parameters:
    ///   - key: The key used to identify the user default in UserDefaults.
    ///   - defaultValue: The default value to use when the user default is not set.
    init(key: String, defaultValue: Value) {
        self.key = key
        self.defaultValue = defaultValue
    }
}

/// A struct containing user default values used in the application.
struct UserDefaultValues {
    // MARK: Wrapped Properties
    
    /// A user default representing whether the app introduction has been seen or not.
    @UserDefault(key: "hasSeenAppIntroduction", defaultValue: false)
    static var hasSeenAppIntroduction: Bool
}

// MARK: Usage

// Setting and retrieving the `hasSeenAppIntroduction` user default value.
UserDefaultValues.hasSeenAppIntroduction = false // Set the value to `false`.
UserDefaultValues.hasSeenAppIntroduction // Retrieve the value, should be `false`.
UserDefaultValues.hasSeenAppIntroduction = true // Set the value to `true`.
UserDefaultValues.hasSeenAppIntroduction // Retrieve the value, should be `true`.