Simpler Coroutine Scope Creation


I’ve been migrating some code from the experimental coroutines to the release version and I find I have to add the same few lines of code to most my classes that spawn new coroutines to make them all CoroutineScoped.

It goes something like this:

class ExampleBefore : CoroutineScope { 
  private val job = Job()
  override val coroutineContext: CoroutineContext get() = job + Dispatchers.IO

Or another dispatcher depending on the class’ needs.

Since I’m lazy and hate duplicating this code around I made myself a new interface for this and a default implementation intended for use as a delegate implementation of the scope interface.

import kotlinx.coroutines.CoroutineDispatcher
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Job
import kotlin.coroutines.CoroutineContext

interface CoroutineScopeAndJob : CoroutineScope {
  val job: Job

class JobBasedScope(val dispatcher: CoroutineDispatcher) : CoroutineScopeAndJob {
  override val job = Job()
  override val coroutineContext: CoroutineContext get() = job + dispatcher

Now in order to make a class able to spawn coroutines in it’s own tree of jobs for easier cancellation I can just delegate the interface to the implementation in a single line like this:

class ExampleAfter : CoroutineScopeAndJob by JobBasedScope(Dispatchers.IO)

Works like a charm, so I thought I’ll share it here for anyone else migrating.

Oh I also made a git gist of it all: