From fcc1290768062334226b98b7cc1d757cd5d8ee08 Mon Sep 17 00:00:00 2001
From: Olivier Blanvillain <olivier.blanvillain@epfl.ch>
Date: Mon, 3 May 2021 16:00:03 +0200
Subject: [PATCH] Add exercises/solutions-4.md
---
exercises/solutions-4.md | 61 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 61 insertions(+)
create mode 100644 exercises/solutions-4.md
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+# Exercise 1 : Implementing map and filter on Futures
+
+```scala
+trait Future[T] { self =>
+ def map[S](f: T => S): Future[S] =
+ new Future[S] {
+ def onComplete(callback: Try[S] => Unit): Unit = self.onComplete {
+ case Success(v) => callback(Success(f(v)))
+ case Failure(e) => callback(Failure(e))
+ }
+ }
+
+ def filter(f: T => Boolean): Future[T] =
+ new Future[T] {
+ def onComplete(callback: Try[T] => Unit): Unit = self.onComplete {
+ case Success(v) =>
+ if (f(v)) callback(Success(v))
+ else callback(Failure(new NoSuchElementException("...")))
+ case Failure(e) => callback(Failure(e))
+ }
+ }
+}
+```
+
+# Exercise 2 : Coordinator / Worker
+
+```scala
+class Coordinator extends Actor {
+ var availableWorkers: List[ActorRef] = Nil
+ var pendingRequests: List[Request] = Nil
+
+ def receive: Receive = {
+ case Ready =>
+ if (pendingRequests.isEmpty) {
+ availableWorkers = availableWorkers :+ sender
+ }
+ else {
+ val request = pendingRequests.head
+ pendingRequests = pendingRequests.tail
+ sender ! request
+ }
+ case request: Request => availableWorkers match {
+ case worker :: rest =>
+ worker ! request
+ availableWorkers = rest
+ case Nil =>
+ pendingRequests = pendingRequests :+ request
+ }
+ }
+}
+
+class Worker(coordinator: ActorRef) extends Actor {
+ coordinator ! Ready
+
+ def receive: Receive = {
+ case Request(f) =>
+ f()
+ coordinator ! Ready
+ }
+}
+```
--
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