Kotlin Class: Inline class email for type-safe email address representation

Last update on August 27 2025 12:39:41 (UTC/GMT +8 hours)

Write a Kotlin program that creates an inline class 'Email' that represents an email address. Use the inline class to enforce type safety.

Pre-Knowledge (Before You Start!)

Before attempting this exercise, you should be familiar with the following concepts:

Inline Classes: A feature in Kotlin that allows wrapping a single value in a class while improving performance by avoiding object overhead.
Type Safety: Ensuring that values are used correctly by restricting them to specific types.
Functions in Kotlin: Understanding how to define and call functions with parameters.
Printing to Console: Using println() to display messages.

Hints (Try Before Looking at the Solution!)

Try to solve the problem using these hints:

Hint 1: Define an inline class named Email that takes a single string parameter.
Hint 2: Create a function named sendEmail() that accepts an Email type parameter.
Hint 3: In the main() function, create an instance of the Email class with an email address.
Hint 4: Pass the email instance to the sendEmail() function and print the email being sent.

Sample Solution:

Kotlin Code:

inline class Email(val value: String)

fun sendEmail(email: Email) {
    println("Sending email to ${email.value}")
}

fun main() {
    val email = Email("[email protected]")
    sendEmail(email)
}

Sample Output:

Sending email to [email protected]

Explanation:

In the above exercise -

We define an inline class "Email" with a single property value of type String. The Email class is marked as inline, which allows it to be used as a wrapper type with improved performance and type safety.
We also define a function "sendEmail(()" that takes an argument of type Email and prints the email address.
In the "main()" function, we create an instance of the "Email" class with the email address "[email protected]". We then pass this instance to the "sendEmail()" function.

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