Instances for Future

Future is largely known to not be referentially transparent. As it starts execution immediately and caches the result.

While it may have been largely necessary for these instances to be in cats before cats-effect, with that solution coming in maturity it may be time for Future instances to be pushed to alleycats.

Imports

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
import cats.implicits._ 

Example 1 - Prints Once on the first line

val future1 : Future[Unit] = Future(println("I printed"))
val futureResult1 : Future[Unit] = (future1, future1).mapN(_ => ())

Example 2 - Prints twice on the second line

def future2: Future[Unit] = Future(println("I printed"))
val futureResult2 : Future[Unit] = (future2, future2).mapN(_ => ())

As you can see we have lost equational reasoning.

What are your thoughts on the future of Future?

Start with the issue's scala.concurrent.Future examples and imports, then review how the Future instances relate to cats-effect and the proposed alleycats placement. Done would require a maintainer decision on whether the instances remain in cats or move, with an agreed scope for any follow-up changes.