Data Classes and Sealed Types

Sealed When

Use when to handle each sealed subclass.

sealed-when `when` pairs naturally with sealed classes because every subclass can be listed.

Sealed When

score
SealedWhen.kt
Replay: real traced execution (multi-file project)
sealed class Level
class LowLevel : Level()
class HighLevel : Level()

fun describe(level: Level): String {
    return when (level) {
        is LowLevel -> "low"
        is HighLevel -> "high"
    }
}

fun main() {
    val score = 8
    val level: Level

    if (score >= 8) {
        level = HighLevel()
    } else {
        level = LowLevel()
    }

    val label = describe(level)

    println("score=$score")
    println("label=$label")
}

sealed class Level
class LowLevel : Level()
class HighLevel : Level()

fun describe(level: Level): String {
    return when (level) {
        is LowLevel -> "low"
        is HighLevel -> "high"
    }
}

fun main() {
    val score = 3
    val level: Level

    if (score >= 8) {
        level = HighLevel()
    } else {
        level = LowLevel()
    }

    val label = describe(level)

    println("score=$score")
    println("label=$label")
}

sealed class Level
class LowLevel : Level()
class HighLevel : Level()

fun describe(level: Level): String {
    return when (level) {
        is LowLevel -> "low"
        is HighLevel -> "high"
    }
}

fun main() {
    val score = 10
    val level: Level

    if (score >= 8) {
        level = HighLevel()
    } else {
        level = LowLevel()
    }

    val label = describe(level)

    println("score=$score")
    println("label=$label")
}

  1. score ← 8

    12fun main() {13    val score→ 8 = 8 //@score=3, 1014    val level: Level

  2. if (score >= 8)

    16if (score8 >= 8) {17    level = HighLevel()18} else {

  3. val label = describe(level)

    22val label = describe(level)

  4. fun describe(level: Level): String

    5fun describe(level: Level): String {6    return when (level) {7        is LowLevel -> "low"8        is HighLevel -> "high"9    }10}

  5. label ← high

    22    val label→ high = describe(level)2324    println("score=$score8")25    println("label=$labelhigh")26}
    outputscore=8
label=high

  1. score ← 3

    12fun main() {13    val score→ 3 = 314    val level: Level

  2. else

    17    level = HighLevel()18} else {19    level = LowLevel()20}

  3. val label = describe(level)

    22val label = describe(level)

  4. fun describe(level: Level): String

    5fun describe(level: Level): String {6    return when (level) {7        is LowLevel -> "low"8        is HighLevel -> "high"9    }10}

  5. label ← low

    22    val label→ low = describe(level)2324    println("score=$score3")25    println("label=$labellow")26}
    outputscore=3
label=low

  1. score ← 10

    12fun main() {13    val score→ 10 = 1014    val level: Level

  2. if (score >= 8)

    16if (score10 >= 8) {17    level = HighLevel()18} else {

  3. val label = describe(level)

    22val label = describe(level)

  4. fun describe(level: Level): String

    5fun describe(level: Level): String {6    return when (level) {7        is LowLevel -> "low"8        is HighLevel -> "high"9    }10}

  5. label ← high

    22    val label→ high = describe(level)2324    println("score=$score10")25    println("label=$labelhigh")26}
    outputscore=10
label=high