Return type depending on parameter type (e.g. Await.ready()) does not work as expected

Question

Scala `Await.ready()` method is defined like this: ``` def ready[T](awaitable: Awaitable[T], atMost: Duration): awaitable.type = ... ``` That is, the return type is a path-dependent type of `awaitable` parameter. I thought that (and IntelliJ IDEA agreed with me) this means that if I pass `Future` to the function, it should return `Future` of the same type, and indeed, it does work in simple cases: ``` val f: Future[Int] = Future { 10 } val ft: Future[Int] = Await.ready(f, ???) ``` This code compiles, that is, `Await.ready()` here really returns `Future[Int]`. However, the following does not work: ``` val f: Future[Int] = Future { 10 } val ft: Future[Int] = Await.ready(f.map(identity), ???) ``` It fails with this error: ``` [error] /Users/netvl/dev/work/sandbox/src/main/scala/circuit/actors/Example.scala:53: type mismatch; [error] found : awaitable.type (with underlying type scala.concurrent.Awaitable[Int]) [error] required: scala.concurrent.Future[Int] [error] val ft: Future[Int] = Aw…

Accepted Answer

The Scala version would be helpful here. With Scala 2.11.1 it works perfectly fine:

```
scala> val f: Future[Int] = Future(10)
f: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@68d0db31

scala> val ft: Future[Int] = Await.ready(f.map(identity), 1.second)
ft: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@68d0db31
```

Return type depending on parameter type (e.g. Await.ready()) does not work as expected

Solution

Problem