Kotlin — Sealed Classes

Basic sealed class

sealed class Result {
    data class Success(val data: String) : Result()
    data class Error(val message: String) : Result()
    object Loading : Result()
}

fun handle(result: Result) = when (result) {
    is Result.Success -> println("Data: ${result.data}")
    is Result.Error -> println("Error: ${result.message}")
    is Result.Loading -> println("Loading...")
}

Sealed interface

sealed interface Shape {
    data class Circle(val radius: Double) : Shape
    data class Rectangle(val width: Double, val height: Double) : Shape
}

fun area(shape: Shape) = when (shape) {
    is Shape.Circle -> Math.PI * shape.radius.pow(2)
    is Shape.Rectangle -> shape.width * shape.height
}

Mini Practice

Write Kotlin code that:

1. Creates a sealed class with data classes
2. Uses when expression for exhaustive matching
3. Creates a sealed interface
4. Demonstrates exhaustive when

Up Next

In the next lesson, you'll learn about Inline Classes — type-safe wrappers.