How to concurrently create Future from Try?

3
votes

The scala Future has a fromTry method which

Creates an already completed Future with the specified result or exception.

The problem is that the newly created Future is already completed. Is it possible to have the evaluation of the Try done concurrently?

As an example, given a function that returns a Try:

def foo() : Try[Int] = {
  Thread sleep 1000
  Success(43)
}

How can the evaluation of foo be done concurrently?

A cursory approach would be to simply wrap a Future around the function:

val f : Future[Try[Int]] = Future { foo() }

But the desired return type would be a Future[Int]

val f : Future[Int] = ???

Effectively, how can the Try be flattened within a Future similar to the fromTry method?

There is a similar question, however the question & answer wait for the evaluation of the Try before constructing the completed Future.

2
multithreadingscalaconcurrencyfuture
As I always say, the Scaladoc is your friend - Future.delegate(Future.fromTry(foo())) - Luis Miguel Mejía Suárez
No, delegate isn't it. You are looking for Future(foo.get) - Dima
@Dima That only works if the Try is Success, not Failure. - Ramón J Romero y Vigil
@RamónJRomeroyVigil nope. It works either way. Try it :) - Dima
@Dima Playing code golf :) I think Luis' swing is right as delegate executes by-name argument on execution context. My swing: Future(foo()).flatMap(Future.fromTry) - Mario Galic

2 Answers

3
votes

Least ceremony is probably:

Future.unit.transform(_ => foo())

Special mention goes to @Dima for the suggestion of Future(foo().get) which is a bit shorter—but might be slightly less readable.

2
votes

Based on the comments,

Scala >= 2.13:

val f : Future[Int] = Future.delegate(Future.fromTry(foo()))

Scala < 2.13:

val f : Future[Int] = Future(foo()).flatMap(Future.fromTry)