Map-backed delegated properties in Kotlin - Mini Project: Build & Apply

Map-backed Delegated Properties in Kotlin

📖 Scenario: You are creating a simple user profile system where user details are stored in a map. You want to access these details as properties of a Kotlin class using map-backed delegated properties.

🎯 Goal: Build a Kotlin class UserProfile that uses a Map to store user data and access it through delegated properties.

📋 What You'll Learn

Create a Map with user data including "name", "age", and "email".

Create a UserProfile class that takes the map as a constructor parameter.

Use map-backed delegated properties to access name, age, and email inside UserProfile.

Print the values of name, age, and email from an instance of UserProfile.

💡 Why This Matters

🌍 Real World

Map-backed delegated properties are useful when you want to store data in a flexible map but access it like normal class properties, such as in configuration settings or user profiles.

💼 Career

Understanding delegated properties and map usage is valuable for Kotlin developers working on Android apps or backend services where dynamic data structures are common.

1

Create the user data map

Create a Map called userData with these exact entries: "name" to "Alice", "age" to 30, and "email" to "[e-mail]".

Kotlin

# Create the userData map with name, age, and email
# Your code here

Need a hint?

Use mapOf to create a map with keys and values.

2

Create the UserProfile class with map parameter

Create a class called UserProfile that takes a Map<String, Any> parameter called data in its primary constructor.

Kotlin

val userData = mapOf("name" to "Alice", "age" to 30, "email" to "[e-mail]")

// Create UserProfile class with a constructor parameter called data
# Your code here

Need a hint?

Define a class with a primary constructor that takes a map parameter.

3

Add map-backed delegated properties

Inside the UserProfile class, add three properties: name, age, and email. Use by data to delegate these properties to the data map.

Kotlin

val userData = mapOf("name" to "Alice", "age" to 30, "email" to "[e-mail]")

class UserProfile(val data: Map) {
    // Add delegated properties name, age, and email here
# Your code here
}

Need a hint?

Use val propertyName: Type by data syntax for map-backed delegation.

4

Create UserProfile instance and print properties

Create an instance of UserProfile called user using userData. Then print user.name, user.age, and user.email each on a new line.

Kotlin

val userData = mapOf("name" to "Alice", "age" to 30, "email" to "[e-mail]")

class UserProfile(val data: Map) {
    val name: String by data
    val age: Int by data
    val email: String by data
}

// Create user instance and print name, age, and email
# Your code here

Need a hint?

Create the UserProfile instance and use println to show each property.