Functional Kotlin

Managing mutable state

The main concern (and nightmare fuel) when we deal with asynchronous code is how to handle mutable state. We covered how to reduce mutable state with a functional style in Chapter 3, Immutability - It's Important. But sometimes it is impossible to use a functional immutable style. Coroutines offer some alternatives to this problem.

In the following example, we'll use several coroutines to update a counter:

import kotlin.system.measureTimeMillissuspend fun repeatInParallel(times: Int, block: suspend () -> Unit) {   val job = launch {      repeat(times) {         launch(coroutineContext) {            block()         }      }   }   job.join()}fun main(args: Array<String>) = runBlocking {   var counter = 0   val time = measureTimeMillis { repeatInParallel(1_000_000) ...