@propertyWrapper declaration in Swift - Mini Project: Build & Apply

Using @propertyWrapper to Manage User Age

📖 Scenario: You are building a simple user profile system where you want to control how the user's age is stored and validated.

🎯 Goal: Create a @propertyWrapper called AgeLimit that ensures the age is always between 0 and 120. Then use it in a User struct to store the user's age safely.

📋 What You'll Learn

Create a @propertyWrapper named AgeLimit

Inside AgeLimit, have a private variable value of type Int

Initialize value with a default age passed in the initializer

Clamp the age value between 0 and 120 in the wrappedValue property

Create a struct User with a property age using the @AgeLimit wrapper

Initialize a User instance with an age and print the age

💡 Why This Matters

🌍 Real World

Property wrappers help keep data clean and safe by controlling how values are stored and changed, useful in apps with user input.

💼 Career

Understanding property wrappers is important for Swift developers to write clean, reusable, and safe code in iOS and macOS apps.

1

Create the @propertyWrapper AgeLimit with a private value

Create a @propertyWrapper named AgeLimit with a private variable value of type Int initialized to 0.

Swift

@propertyWrapper
struct AgeLimit {
    // Your code here
}

Need a hint?

Use @propertyWrapper before the struct declaration. Inside, declare private var value: Int = 0.

2

Add initializer to AgeLimit to set initial age value

Add an initializer to AgeLimit that takes an Int parameter called wrappedValue and sets value to it.

Swift

@propertyWrapper
struct AgeLimit {
    private var value: Int = 0
    
    // Add initializer here
}

Need a hint?

Write init(wrappedValue: Int) and assign wrappedValue to value.

3

Implement wrappedValue property to clamp age between 0 and 120

Add a computed property wrappedValue of type Int that returns value clamped between 0 and 120. When setting, update value with the clamped new value.

Swift

@propertyWrapper
struct AgeLimit {
    private var value: Int = 0
    
    init(wrappedValue: Int) {
        self.value = wrappedValue
    }
    
    // Add wrappedValue computed property here
}

Need a hint?

Use a computed property with get and set. Clamp values using conditional expressions.

4

Create User struct using @AgeLimit and print age

Create a struct User with a property age using the @AgeLimit wrapper. Initialize a User instance with age 150 and print user.age.

Swift

@propertyWrapper
struct AgeLimit {
    private var value: Int = 0
    
    init(wrappedValue: Int) {
        self.value = wrappedValue
    }
    
    var wrappedValue: Int {
        get { value  120 ? 120 : value) }
        set { value = newValue  120 ? 120 : newValue) }
    }
}

// Create User struct and print age
// Your code here

Need a hint?

Define User with @AgeLimit var age: Int. Create user with age 150 and print user.age.