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  1. PO
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    <p>I wanted to try out the new <a href="https://github.com/scala/async" rel="nofollow">Async API</a> and this was a nice test. In fact there is an example that is very close to your use case on the Async Github home page.</p> <p>Async is a <a href="http://docs.scala-lang.org/sips/pending/async.html" rel="nofollow">SIP</a> and will likely be part of standard Scala at some point. </p> <p>Besides using <code>await</code> the idea here is that you have an abstract <code>add()</code> method that uses asynchronous logic behind the scenes. That way it is hidden from the <code>Calculator</code> developers. </p> <p>Personally I would add an async version of the API too so <code>Future</code>s could be passed out of the <code>Calculator</code> to be composed with other <code>Future</code>s.</p> <pre><code>trait Calculator { def hardToCalculate1: Int def hardToCalculate2: Int def hardToCalculate3: Int def add(a: =&gt; Int, b: =&gt; Int): Int def result1 = add(hardToCalculate1, hardToCalculate2) def result2 = add(hardToCalculate2, hardToCalculate3) def result3 = add(hardToCalculate1, hardToCalculate3) } object So17677728 extends App with Calculator { override def add(a: =&gt; Int, b: =&gt; Int): Int = { val start = System.currentTimeMillis val res = Await.result(asyncAdd(a, b), 2000 millis) val end = System.currentTimeMillis println(s"Total time: ${end - start} ms") res } def asyncAdd(a: =&gt; Int, b: =&gt; Int): Future[Int] = { async { val fa = Future(a) val fb = Future(b) await(fa) + await(fb) } } val random = Random val maxSleep = 1000 def hardToCalculate1: Int = htc(1) def hardToCalculate2: Int = htc(2) def hardToCalculate3: Int = htc(3) def htc(n: Int) = { val sleepMs = random.nextInt(1000) println(s"$n sleeping for $sleepMs ms") Thread.sleep(sleepMs) println(s"$n done sleeping") n } println(s"result1: $result1\n") println(s"result2: $result2\n") println(s"result3: $result3\n") } </code></pre> <p>Output</p> <pre><code>1 sleeping for 438 ms 2 sleeping for 244 ms 2 done sleeping 1 done sleeping Total time: 497 ms result1: 3 3 sleeping for 793 ms 2 sleeping for 842 ms 3 done sleeping 2 done sleeping Total time: 844 ms result2: 5 3 sleeping for 895 ms 1 sleeping for 212 ms 1 done sleeping 3 done sleeping Total time: 896 ms result3: 4 </code></pre> <p>Alternatively in <code>add</code> you could <code>Future</code>s and a for comprehension instead of <code>async</code>/<code>await</code>.</p>
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    1. POSatisfying Abstract Trait Requirements with Futures
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    1. COThanks. Still beating my head on this one. It seems like I should be able to create some kind of wrapper class that allows me to use the simple, straightforward functions within Calculator, but supply the hard values (and retrieve the results) asynchronously.
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    2. COActually, my bad, using asynchronicity in Calculator would be good because the `hardToCalculate` methods could be done in parallel. I've replaced my answer.
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    3. COThanks for the intro to async ... that may help with what I'm trying to do. I don't want to write asynchronous versions of all of the math that might be done within `Calculator`. The point is to try to keep that code as straightforward and easy-to-test as possible for people who don't need to understand how async stuff works. But, the async way of composing things definitely as some advantages over pure Futures -- need to spend some time with it.
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