API design question - which would you use to pass ...

# coroutines

[zak.taccardi]

API design question - which would you use to pass around a read-only value that gets initialized once and cached?

1. suspend () -> T
2. Deferred<T>

Vote 1️⃣ for suspend fun () -> T or 2️⃣ for Deferred<T>

[zak.taccardi]

I see suspend () -> T as a more abstract approach, but it requires more boilerplate + some extra anonymous classes

[zak.taccardi]

Deferred<T> has a lot less boilerplate to implement, more clearly indicates that the value will be cached, but it exposes its underlying Job API, which a caller could accidentally cancel

[octylFractal]

if you're worried about the cancellation, just create a separate CompletableDeferred that's not part of the job.

[zak.taccardi]

CompletableDeferred extends Deferred so it’s worse. This isn’t an API that you would want to allow callers to be able to complete. It’s read only

[octylFractal]

I don't mean return it -- I mean use it to prevent cancellation of the underlying job

[octylFractal]

you'd still return Deferred<T>, but internally you would hand-off the value to create a gap

[zak.taccardi]

oh, very interesting

[Dominaezzz]

Interface version of option 1 I think.

[zak.taccardi]

I’m not a fan of the interface approach as that is less flexible

[louiscad]

I'm using top level functions to initialize top level `val`s of the SuspendLazy type: https://github.com/LouisCAD/Splitties/blob/develop/modules/coroutines/src/commonMain/kotlin/splitties/coroutines/SuspendLazy.kt

https://github.com/LouisCAD/Splitties/blob/develop/modules/coroutines/src/jvmMain/kotlin/splitties/coroutines/SuspendLazyJVM.kt

[zak.taccardi]

interesting idea, but I would like to avoid introducing a custom type

[louiscad]

Well, you can make the top level val private, and make a top level suspending function getting the value from it.