Custom validation property wrappers in Swift - Mini Project: Build & Apply

Custom Validation Property Wrappers

📖 Scenario: You are building a simple user registration form in Swift. You want to make sure the user's input is valid before saving it.

🎯 Goal: Create a custom property wrapper to validate a username so it is at least 5 characters long. Use this property wrapper in a User struct and print the username if it is valid.

📋 What You'll Learn

Create a custom property wrapper called ValidatedUsername

The property wrapper should check that the username is at least 5 characters long

Create a User struct with a username property using the ValidatedUsername wrapper

Create an instance of User with the username "SwiftDev"

Print the username from the User instance

💡 Why This Matters

🌍 Real World

Property wrappers help keep your code clean by centralizing validation logic for user input or data models.

💼 Career

Understanding property wrappers and validation is useful for Swift developers building safe and maintainable apps.

1

Create the ValidatedUsername property wrapper

Create a property wrapper called ValidatedUsername with a wrappedValue property of type String. Initialize wrappedValue with an empty string.

Swift

# Create the ValidatedUsername property wrapper
# Your code here

Need a hint?

Use @propertyWrapper before the struct. Define wrappedValue as a String property with default empty string.

2

Add validation logic to ValidatedUsername

Modify the ValidatedUsername property wrapper to accept an initial wrappedValue in its initializer. Add validation so that if the username is shorter than 5 characters, it sets wrappedValue to an empty string.

Swift

@propertyWrapper
struct ValidatedUsername {
    var wrappedValue: String

    // Add initializer with validation
    // Your code here
}

Need a hint?

Use an initializer init(wrappedValue: String). Check the length with wrappedValue.count. Assign accordingly.

3

Create the User struct using ValidatedUsername

Create a struct called User with a property username that uses the @ValidatedUsername property wrapper.

Swift

@propertyWrapper
struct ValidatedUsername {
    var wrappedValue: String

    init(wrappedValue: String) {
        if wrappedValue.count >= 5 {
            self.wrappedValue = wrappedValue
        } else {
            self.wrappedValue = ""
        }
    }
}

// Create User struct with username property
// Your code here

Need a hint?

Define struct User. Add @ValidatedUsername before var username: String.

4

Create a User instance and print the username

Create a constant user of type User with the username "SwiftDev". Then print user.username.

Swift

@propertyWrapper
struct ValidatedUsername {
    var wrappedValue: String

    init(wrappedValue: String) {
        if wrappedValue.count >= 5 {
            self.wrappedValue = wrappedValue
        } else {
            self.wrappedValue = ""
        }
    }
}

struct User {
    @ValidatedUsername var username: String
}

// Create user instance and print username
// Your code here

Need a hint?

Create let user = User(username: "SwiftDev"). Then print(user.username).