Kotlin 'when' statement vs Java 'switch'

Question

Pattern matching in Kotlin is nice and the fact it does not execute the next pattern match is good in 90% of use cases.

In Android, when database is updated, we use Java switch property to go on next case if we do not put a break to have code looking like that:

switch (oldVersion) {     case 1: upgradeFromV1();     case 2: upgradeFromV2();      case 3: upgradeFromV3(); } 

So if someone has an app with version 1 of the DB and missed the app version with DB v2, he will get all the needed upgrade code executed.

Converted to Kotlin, we get a mess like:

when (oldVersion) {     1 -> {         upgradeFromV1()         upgradeFromV2()         upgradeFromV3()     }     2 -> {         upgradeFromV2()         upgradeFromV3()     }     3 -> {         upgradeFromV3()     } } 

Here we have only 3 versions, imagine when DB reaches version 19.

Anyway to makes when acting in the same way then switch? I tried to continue without luck.

Answer 1

Simple but wordy solution is:

if (oldVersion <= 1) upgradeFromV1() if (oldVersion <= 2) upgradeFromV2() if (oldVersion <= 3) upgradeFromV3() 

Another possible solution with function references:

fun upgradeFromV0() {} fun upgradeFromV1() {} fun upgradeFromV2() {} fun upgradeFromV3() {}  val upgrades = arrayOf(::upgradeFromV0, ::upgradeFromV1, ::upgradeFromV2, ::upgradeFromV3)  fun upgradeFrom(oldVersion: Int) {     for (i in oldVersion..upgrades.lastIndex) {         upgrades[i]()     } } 

Answer 2

edit: Original response below. Here's what I'm currently doing:

fun upgrade() {     fun upgradeFromV1() { /* Do stuff */ }     fun upgradeFromV3() { /* Do stuff */ }      tailrec fun upgradeFrom(version: Int): Unit = when (version) {         LATEST_VERSION -> {             Config.version = version         } 1 -> {             upgradeFromV1()             upgradeFrom(2)         } in 2..3 -> {             upgradeFromV3()             upgradeFrom(4)         } else -> {             Log("Uncaught upgrade from $version")             upgradeFrom(version+1)     }      upgradeFrom(Config.version) } 

---

Here's a variation on the answer @C.A.B. gave:

fun upgrade(oldVersion: Int) {     when (oldVersion) {         latestVersion -> return         1 -> upgradeFromV1()         2 -> upgradeFromV2()         3 -> upgradeFromV3()     }     upgrade(oldVersion + 1) }