WrappedValue and projectedValue in Swift - Mini Project: Build & Apply

Using WrappedValue and projectedValue in Swift Property Wrappers

📖 Scenario: Imagine you are building a simple app that tracks the progress of tasks. You want to create a custom property wrapper that stores a task's progress as a percentage and also provides a message about the progress.

🎯 Goal: Build a Swift program that uses a property wrapper with wrappedValue to store the progress percentage and projectedValue to provide a progress message.

📋 What You'll Learn

Create a property wrapper named ProgressTracker with wrappedValue and projectedValue

Use wrappedValue to store an integer progress percentage

Use projectedValue to return a string message about the progress

Create a struct Task with a property progress using the ProgressTracker wrapper

Print the progress percentage and the progress message

💡 Why This Matters

🌍 Real World

Property wrappers help you add reusable behavior to properties, such as validation, formatting, or extra info, which is common in app development.

💼 Career

Understanding property wrappers and their wrapped and projected values is important for Swift developers working on iOS or macOS apps to write clean and reusable code.

1

Create the ProgressTracker property wrapper

Create a property wrapper named ProgressTracker with a wrappedValue property of type Int initialized to 0.

Swift

# Create the ProgressTracker property wrapper with wrappedValue
// Your code here

Need a hint?

Use @propertyWrapper before the struct. Define wrappedValue as an Int with default 0.

2

Add projectedValue to provide a progress message

Inside ProgressTracker, add a computed property projectedValue of type String that returns "Progress is X%" where X is the current wrappedValue.

Swift

@propertyWrapper
struct ProgressTracker {
    var wrappedValue: Int = 0
    
    // Add projectedValue computed property here
    // Your code here
}

Need a hint?

Define projectedValue as a computed property returning a string with the current wrappedValue.

3

Create Task struct using ProgressTracker

Create a struct named Task with a property progress that uses the @ProgressTracker property wrapper.

Swift

@propertyWrapper
struct ProgressTracker {
    var wrappedValue: Int = 0
    
    var projectedValue: String {
        "Progress is \(wrappedValue)%"
    }
}

// Create Task struct with progress property using @ProgressTracker
// Your code here

Need a hint?

Define struct Task with a property progress using @ProgressTracker.

4

Set progress and print wrappedValue and projectedValue

Create an instance of Task named myTask. Set myTask.progress to 75. Then print myTask.progress and myTask.$progress.

Swift

@propertyWrapper
struct ProgressTracker {
    var wrappedValue: Int = 0
    
    var projectedValue: String {
        "Progress is \(wrappedValue)%"
    }
}

struct Task {
    @ProgressTracker var progress: Int
}

// Create myTask, set progress to 75, and print progress and projectedValue
// Your code here

Need a hint?

Create myTask, assign 75 to progress, then print myTask.progress and myTask.$progress.