Property wrappers with configuration in Swift - Mini Project: Build & Apply

Property wrappers with configuration

📖 Scenario: Imagine you are building a simple app that tracks user settings. You want to make sure some settings have default values and can be easily configured.

🎯 Goal: You will create a property wrapper that allows setting a default value and then use it to manage user settings with configurable defaults.

📋 What You'll Learn

Create a property wrapper called DefaultValue that stores a wrapped value.

Add a configuration property called defaultValue to the wrapper.

Use the property wrapper on a struct's properties with different default values.

Print the values of the properties to see the defaults in action.

💡 Why This Matters

🌍 Real World

Property wrappers help manage default values and add behavior to properties in apps, making code cleaner and easier to maintain.

💼 Career

Understanding property wrappers is useful for Swift developers working on iOS or macOS apps to write reusable and configurable code.

1

Create the property wrapper with a default value

Create a property wrapper called DefaultValue that has a generic type Value. Inside it, declare a variable wrappedValue of type Value. Add an initializer that accepts a parameter called defaultValue of type Value and sets wrappedValue to this defaultValue.

Swift

# Create the property wrapper DefaultValue with a wrappedValue and an initializer
# Your code here

Need a hint?

Use @propertyWrapper before the struct. The initializer should set wrappedValue to the defaultValue parameter.

2

Create a struct with properties using the wrapper

Create a struct called UserSettings. Inside it, declare two properties: username and isDarkMode. Use the @DefaultValue property wrapper on both. Set the default value for username to "Guest" and for isDarkMode to false.

Swift

@propertyWrapper
struct DefaultValue {
    var wrappedValue: Value
    
    init(defaultValue: Value) {
        self.wrappedValue = defaultValue
    }
}

// Create UserSettings struct with two properties using @DefaultValue
# Your code here

Need a hint?

Use the property wrapper syntax @DefaultValue(defaultValue: ...) before each property.

3

Create an instance and access the properties

Create a variable called settings and assign it a new instance of UserSettings. Then, access the properties username and isDarkMode from settings.

Swift

@propertyWrapper
struct DefaultValue {
    var wrappedValue: Value
    
    init(defaultValue: Value) {
        self.wrappedValue = defaultValue
    }
}

struct UserSettings {
    @DefaultValue(defaultValue: "Guest")
    var username: String
    
    @DefaultValue(defaultValue: false)
    var isDarkMode: Bool
}

// Create an instance of UserSettings called settings
# Your code here

Need a hint?

Create settings as UserSettings(). Access properties with dot notation like settings.username.

4

Print the property values

Print the values of settings.username and settings.isDarkMode using two separate print statements.

Swift

@propertyWrapper
struct DefaultValue {
    var wrappedValue: Value
    
    init(defaultValue: Value) {
        self.wrappedValue = defaultValue
    }
}

struct UserSettings {
    @DefaultValue(defaultValue: "Guest")
    var username: String
    
    @DefaultValue(defaultValue: false)
    var isDarkMode: Bool
}

var settings = UserSettings()
let user = settings.username
let darkMode = settings.isDarkMode

// Print username and isDarkMode values
# Your code here

Need a hint?

Use print(settings.username) and print(settings.isDarkMode) to show the values.