Lifting a Future[T] into a Future[Either[Throwable, T]]

[Chris Marshall]

The new concurrent Future class ( http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/index.html#scala.concurrent.Future) should (I think) have a mechanism to lift a Future[T] into a Future[Either[Throwable, T]] (the method could be called "liftEither", or just "e").

The reason that this is useful is that it means we can go through the following process:

CC[Future[T]] ~> CC[Future[Either[Throwable, T]]] ~> CC[Future[ValidationNEL[Throwable, T]] ~> Future[ValidationNEL[Throwable, CC[T]]]

It also means that the future can be used in a for-comprehension without "silently" ignoring failure:

for (e <- intFuture.e) yield e.right.map( ... etc )

Is this worthy of an RFE? It's an incredibly simple library addition

Chris

[Josh Suereth]

Might be more useful to have a general "mapResult" that looks like:

def mapResult[B](f: Either[Throwable,T] => Either[Throwable,B]): Future[B]

That way you could lift the result directly into a Validation if you wanted...

[√iktor Ҡlang]

def lift[T](f: Future[T]): Future[Either[Throwable, T]] = f map Right.apply recover { case t => Left(t) } ?

Cheers,

√

 

Chris

--
Viktor Klang

Akka Tech Lead

Typesafe - The software stack for applications that scale

Twitter: @viktorklang

[Kevin Wright]

That's what I do :)

It's the only way to get sane behaviour from Future.sequence/traverse

[Chris Marshall]

Does that count as agreement that it's a good idea to add?

---

Date: Fri, 1 Jun 2012 15:16:12 +0200
Subject: Re: [scala-user] Lifting a Future[T] into a Future[Either[Throwable, T]]
From: viktor...@gmail.com
To: oxbow...@hotmail.com
CC: scala...@googlegroups.com

[√iktor Ҡlang]

On Fri, Jun 1, 2012 at 3:49 PM, Chris Marshall <oxbow...@hotmail.com> wrote:

Does that count as agreement that it's a good idea to add?

What should happen if you lift a Future[Either[Throwable, T]]?

[Chris Marshall]

You should get a Future[Either[Throwable, Either[Throwable, T]]] and it will be your own fault if you do.

---

Date: Fri, 1 Jun 2012 15:59:59 +0200