Are continuations in Kotlin usable yet? Any examples available?

Question

There is an package in Kotlin for continuations, but it's marked as experimental. There is no documentation other than the API, and no tutorial or examples anywhere that I could find. Does anyone know if it's already usable? What would be an example of its usage?

Answer 1

The Continuation interface is a part of coroutines support API in the standard library. You can start exploring the coroutines from the documentation page, or from the kotlinx.coroutines library repository, which contains an extensive coroutine programming guide.

Coroutines are experimental in Kotlin 1.1 and 1.2, but there was an announcement that they are going to stabilize in 1.3.

Answer 2

When you say "continuations", you actually mean "coroutines". Continuation is a part of that story.

kotlin-coroutines-informal by the JetBrains team is a great resource to start you off with coroutines. If you're looking to use them for async programming on Android, especially take note of the section on wrapping the callbacks which your existing async API provides, turning the existing Java function calls into Kotlin suspend funs.

About the status of experimental, check out Roman Elizarov's answer to that question. Here's a highlight:

Kotlin coroutines can and should be used in production. That was the chief reason to officially release them in Kotlin 1.1. Having released them, the JetBrains team had committed to maintain backwards compatibility with respect to any changes that are introduced to them in the minor releases as they evolve, while allowing people to safely try them in complex production applications.

There is absolutely no reason to wait for 1.3 to start using coroutines. Whatever you write today will work into the foreseeable future with no changes and, on top of that, it will be very easy to switch from kotlinx.coroutines.experimental to kotlinx.coroutines after the release. The APIs are already very stable and most of the changes are now in the area of channels and actors.