Functions `coroutineScope`, `withContext`, `withTimeout` and `supervisorScope` have very similar be...

# coroutines

[marcinmoskala]

Functions coroutineScope, withContext, withTimeout and supervisorScope have very similar behavior and this group should have a name. In some places they are referenced as "Scoping functions", but I understand this can be confused with "Scope functions". What are your feelings about that? I am considering naming them "Coroutine scope function" or "Coroutine scoping functions".

[Joffrey]

Mmh I don't believe they have similar behaviour. coroutineScope and supervisorScope create a scope to allow launching coroutines, and suspend until those child coroutines terminate. These 2 could be grouped. The 2 others don't provide a scope, so they have quite different usage patterns and I don't quite get the need for a name that would encompass them as well. withTimeout is just a suspend function like any other, and I don't see it as related to withContext

[marcinmoskala]

@Joffrey Show me, because as far as I tested, there is no difference between coroutineScope, withContext(EmptyCoroutineContext) and withTimeout(Long.MAX_VALUE). They all create scope.

[Joffrey]

Apologies, then. I was answering from the top of my head, and withTimeout and withContext actually do provide a scope. That being said, they popped in such different contexts in my experience that I actually never had to consider these 4 as a group.
And in particular, I never used withTimeout or withContext to actually start coroutines - just to control the timeout of some suspending code, or change the context. Starting a coroutine with withContext would be equivalent to just pass that context to the actual coroutine builder.

[julian]

This is very interesting. I never would have thought withTimeout created a new scope. But I'm glad to see confirmation that withContext does create a new scope, rather than "just" modify context.

[julian]

@marcinmoskala Do you cover this in your book on coroutines?

[marcinmoskala]

Yes, this is the current state of the chapter about both of them:
https://kt.academy/article/cc-scoping-functions

[julian]

Great! Just bought it!

[julian]

I'm about half-way through Kotlin Coroutines by @marcinmoskala. Really, really good. If you want a deep, thorough, and well-organized understanding of coroutines, there's no better single resource available. I know this because I've been looking for something like this for a couple of years. Highly recommend.