Kotlin·Kotlin from syntax to a coroutine app

Classes and data classes

Model data with data classes, sealed types and properties.

Beginner 13 min read Lesson 5 of 300 Challenge included

What you will be able to do

Use data class for value-like data.
Use sealed class for a closed set of states.
Use copy for immutable updates.
Use when exhaustively over sealed types.

In plain English

A data class generates equals, hashCode, toString and copy. Sealed classes model a closed set of states, which pairs perfectly with exhaustive when expressions.

Models.ktKotlin

data class User(val id: String, val name: String)

sealed class Result {
    data class Ok(val value: String) : Result()
    data class Error(val message: String) : Result()
}

fun render(result: Result) = when (result) {
    is Result.Ok -> result.value
    is Result.Error -> result.message
}

Your turn

Copy a data class

Easy

Create a copy of a user with the name changed to Ada.

KOTLIN · starter

user.copy()

Check your understanding before moving on.

Knowledge checkQuestion 1

Which class type is ideal for a closed set of states?

Select an answer to continue

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