Is there any simple way to implement `Deferred` in...

# coroutines

[tapac]

Is there any simple way to implement Deferred interface? I was trying to delegate that interface to an instance returned by async function, but it doesn't work well.

class MyDeferred<T>(val original: Deferred<T>) : Deferred<T> by original

MyDeferred(async{ ...} )

I want to be able to call some code on async completition or execption, maybe there is another way?

[Adam Powell]

what are you trying to do more specifically?

[Adam Powell]

if you control the code inside the async {} block,

async {
  try {
    stuff()
  } finally {
    codeToRunOnCompletion()
  }
}

[Adam Powell]

if you don't,

try {
  theDeferred.await()
} catch (e: TheExceptionThrown) {
  doStuffWith(e)
}

since many things may .await() on a Deferred and respond when the underlying async is done

[tapac]

I want to make function which will return Deferred with provided fcuntion. That deferred should execute function and then do some additional work on complete or another code on exception.
Like

fun <T>  executeAsync(body: ()->T) : MyDeferred<T> {
}

[tapac]

I want to allow users to use all standard functions which works with Deferred like awaitAll

[octylFractal]

just do the above, and if you need to wrap it in another async {} block, do so.

[tapac]

I want to have special extension for MyDeferred which will chain executions and execute additional code only once.

fun <T, R> MyDeferred<T>.and(body: (T) -> R) : MyDeferred<R>

[octylFractal]

why not just:

suspend fun <T, R> Deferred<T>.and(body: suspend (T) -> R) = async { body(await()) }

[octylFractal]

really sounds like you want a Flow though

[Dico]

You can also just do deferred.invokeOnCompletion { .... }

[Dico]

Doesn't seem like the right tool for your use case

[Dico]

Coroutines are designed explicitly to avoid the pattern that you're trying to create and use

[Dico]

If you want to have map and all those operators, you can indeed use Flow or you can even use Java's CompletableFuture. You can add the kotlinx-coroutines-jdk8 as a dependency and call Deferred.asCompletableFuture() I think.