Scala the language matters
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The document provides an overview of Scala training covering key language features including functions, implicits, monads, and actors. It discusses high order functions, implicit conversions, the Try and Option monads for error handling, and how actors provide thread-safe concurrency through message passing and defined behaviors. Code examples are given for implementing REST APIs using implicits, composing monadic operations, and defining actor classes and messages. References for further learning about Scala and functional programming concepts are also listed.
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Scala the language matters
- 1. SCALA TRAINING the language matters 1
- 2. Agenda • Function • Implicit • Monad • Actor
- 3. Language features - functions • high order function 3
- 4. Language - Implicit • implicit convention
- 5. Language - Implicit val personJson = """{ "name": "Jason" }”"" val r1 = httpClient(Request( GET, new URI("http://api.rest.org/person/"), Map(), None)) val r2 = httpClient(Request( POST, new URI("http://api.rest.org/person/"), Map(), Some(personJson))) val id = r2.headers(“X-Person-Id").head val r3 = httpClient(Request( GET, new URI("http://api.rest.org/person/" + id), Map(), None)) val r4 = httpClient(Request( GET, new URI("http://api.rest.org/person/"), Map(), None)) val r5 = httpClient(Request( DELETE, new URI("http://api.rest.org/person/" + id), Map(), None))
- 6. Language - Implicit using(_ url "http://api.rest.org") { implicit rb => GET / "person" asserting (StatusCode === Status.OK, BodyAsPersonList === EmptyList) val id = POST / "person" body personJson asserting (StatusCode === Status.Created) returning (header(“X-Person-Id")) GET / "person" / id asserting (StatusCode === Status.OK, BodyAsPerson === Jason) GET / "person" asserting (StatusCode === Status.OK, BodyAsPersonList === Seq(Jason)) DELETE / "person" / id asserting (StatusCode === Status.OK) GET / "person" asserting (StatusCode === Status.OK, BodyAsPersonList === EmptyList) }
- 7. Language Feature - Monad sealed abstract class Try[+T] case class Success[+T](value: T) case class Failure[+T](exception: Throwable) case abstract class Option[T] case class Some[T] case object None extends Option[Nothing] {//…}
- 8. Language Feature - Monad //in User def findById(id: Long):Try[User] = { //Success(user) or Failure(e) } //in Post def findByUser(user: User):Try[List[Post]] = { //Success(posts)or Failure(e) } val posts: Try[List[Post]] = User.findById(userId).map { user => Post.findByUser(user) } posts match { case Success(p) => render(p) case Failure(e) => error(e) }
- 9. Language features - Monad import Math.abs type Birds = Int type Pole = (Birds, Birds) def landLeft(n: Int, p: Pole):Option[Pole] = p match { case (left, right) if abs(left + n - right) < 4 => Some(left + n, right) case _ => None } def landRight(n: Int, p: Pole) = p match { case (left, right) if abs(left - n - right) < 4 => Some(left , right + n) case _ => None } val result = landLeft(1, (0, 0)). flatMap{ landLeft(2,_:Pole) }. flatMap{ landRight(5, _:Pole) } println(result) 9
- 10. Language Features - Actor • a small compute unit, including: • behaviour • state • messaging
- 11. Language Features - Actor • rules of when a actor received a message: • create a new actor • send message to a new actor • define behaviour when next message arrived • the most important feature • a actor is always thread safe • concurrent is multiple actor’s behaviour
- 12. Language Features - Actor class MyActor extends Actor { def receive = { case MsgType1 => //do something case MsgType2 => //do something else } } val actorRef = system.actorOf[Props[MyActor]] actorRef ! MsgType1
- 13. References • http://twitter.github.io/scala_school/zh_cn/ index.html • http://twitter.github.io/effectivescala/index-cn.html • http://typesafe.com/blog/all • http://www.cakesolutions.net/teamblogs • http://adit.io/posts/2013-04-17- functors,_applicatives,_and_monads_in_pictures.html 13