Sealed Class

• Used to represent a restricted class hierarchy (useful for when expressions).
• All subclasses must be declared in the same file.
• Constructor is private by default
• Can have functions and abstract functions which the subclasses can implement

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

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