Scala for the doubters

Scala overview and comparison with Java 8

Transcript

1. Scala for the doubters Max Klyga @Neku42
2. –James Gosling “If
3. Scala
4. –James Iry, “A Brief, Incomplete, and Mostly Wrong History of Programming Languages” “A
5. Scala OOP FP
7. Lightweight syntax object Main extends Application { val phonebook = Map( "Alice" -> "212-34-56", "Bob" -> "265-43-21" ) phonebook += ("Carl" -> "298-76-54") println(phonebook("Alice")) for (i <- 1 to 10) { println(i) } } Scala
8. Lightweight syntax public class Person { private String firstName; private String lastName; String getFirstName() { return firstName; } void setFirstName(String firstName) { this.firstName = firstName; } String getLastName() { return lastName; } void setLastName(String lastName) { this.lastName = lastName; } int hashCode() { .... } boolean equals(Object o) { .... } } Java
9. Lightweight syntax case class Person(var firstName:String, var lastName:String) Scala
10. Lightweight syntax boolean hasUpperCase = false; for (int i = 0; i < name.length(); ++i) { if (Character.isUpperCase(name.charAt(i))) { hasUpperCase = true; break; } } Java
11. Lightweight syntax val hasUpperCase = name.exists(_.isUpperCase) Scala
12. Lightweight syntax Predicate<Character> isUpperCase = new Predicate<Character>() { public Character apply(Character ch) { return Character.isUpperCase(ch); } }; boolean hasUpperCase = Iterables.any(Lists.charactersOf(name), isUpperCase); Java + Guava
13. Lightweight syntax Predicate<Character> isUpperCase = (ch) -> Character.isUpperCase(ch); boolean hasUpperCase = Iterables.any(Lists.charactersOf(name), isUpperCase); Java 8 + Guava
14. Lightweight syntax boolean hasUpperCase = name.chars().anyMatch((ch) -> Character.isUpperCase(ch)); Java 8
15. Lightweight syntax boolean hasUpperCase = name.chars().anyMatch((ch) -> Character.isUpperCase(ch)); Java 8 Scala val hasUpperCase = name.exists(_.isUpperCase)
16. Lambdas Java 8 •Can only access final variables •Cannot mutate variables in outer scope Scala •Can access any variables •Can mutate any accessible variables
17. Traits Java 8 •Can define default methods in interfaces (Java 9 allows private methods) •“Diamond” inheritance is forbidden Scala •No restrictions on method implementation •Method invocation chain determined by inheritance order
18. Composable Everything is an expression
19. Composable var x:Int if (…) { x = 10 } else { x = 0 }
20. Composable val x = if (…) { 10 } else { 0 }
21. Composable var x = List[Int]() for (i <- 1 to 10) { x = i :: x }
22. Composable var x = for (i <- 1 to 10) { yield i }
23. Composable Everything is an expression if for while try match
24. Composable Things nest
25. Composable import com.dull.lib class Eggs { import org.cool.lib def bacon { import org.other.cool.lib … } }
26. Composable class Eggs { def bacon { def inner(…) { def innerer { … } … } … } }
27. Pattern matching sealed abstract class ChatProtocol case class Message(userId:Int, text:String) extends ChatProtocol case class Join(userId:Int, name:String) extends ChatProtocol case class Leave(userId:Int) extends ChatProtocol command match { case Message(id, text) => println(s"${users(id)}: ${text}") case Join(id, name) => { users += (id, name) println(s"${name} joined") } case Leave(id) => { println(s"${users(id)} left") users -= id } }
28. REPL Java 9 will finally get it too
29. So much more • Everything is an object • Limited type inference • Operator overloading (Everything is a method) • Algebraic data types • Partial functions • Tuples • Value classes
31. –Alan Perlis “Syntactic
35. Implicits • Conversions • Extension methods via Rich Interface Pattern • Remove boilerplate code
36. Implicits • Conversions • Extension methods via Rich Interface Pattern • Remove boilerplate code
37. Generic code • Partial application • Variance annotations • Implicits • Macros
38. With great power comes great responsibility
39. Sleep of reason produces monsters
40. Operator overloading abuse val intermediateHandler = (:/(host, port) / target <<? params >:> identity) https://github.com/dispatch/reboot def root = jsonObj | jsonArray def jsonObj = "{" ~> repsep(objEntry, ",") <~ "}" ^^ { case vals:List[_] => JSONObject(Map(vals:_*)) } def jsonArray = "[" ~> repsep(value, ",") <~ "]" ^^ { case vals:List[_] => JSONArray(vals) } def objEntry = stringVal ~ (":" ~> value) ^^ { case x ~ y => (x, y) } https://github.com/scala/scala-parser-combinators Unicode operators in ScalaZ: ≠ ∋ ≯ ★ ∅
41. Learning Scala will make you a better Java programmer
42. Learning Scala will make you a better Java programmer • Data transformation pipeline instead of CRUD • “Sane” error handling, data validation http://fsharpforfunandprofit.com/rop/ • Computation and data composition For comprehensions (Monads …)
43. –Paul Graham “you
44. The Python Paradox
45. The Scala Paradox
46. Why use Scala? • eDSL • Parsers • Distributed computing infrastructure
47. eDSL val orders = List[Order]( // use the default pricing strategy new Order to buy(200 sharesOf "GOOGLE") maxUnitPrice 300 using defaultPricing, // use a custom pricing strategy new Order to sell(200 bondsOf "Sun") maxUnitPrice 300 using { (qty, unit) => qty * unit - 500 } ) http://debasishg.blogspot.com/2008/05/designing-internal- dsls-in-scala.html
48. eDSL class HelloWorldSpec extends Specification { def is = s2""" This is a specification for the 'Hello world' string The 'Hello world' string should contain 11 characters $e1 start with 'Hello' $e2 end with 'world' $e3 """ def e1 = "Hello world" must haveSize(11) def e2 = "Hello world" must startWith("Hello") def e3 = "Hello world" must endWith("world") } https://etorreborre.github.io/specs2/
49. eDSL object SquareRoot extends Baysick { def main(args:Array[String]) = { 10 PRINT "Enter a number" 20 INPUT 'n 30 PRINT "Square root of " % "'n is " % SQRT('n) 40 END RUN } } https://github.com/fogus/baysick
51. Java ❤ Scala
52. Java ❤ Scala • Scala Maven plugin - http://davidb.github.io/scala- maven-plugin/
53. Learn more • Twitter Scala school http://twitter.github.io/scala_school/ • Scala for the Impatient http://www.horstmann.com/scala/ • Programming in Scala http://www.artima.com/shop/programming_in_scala_2ed • Functional Programming in Scala http://manning.com/bjarnason/
54. Questions Max Klyga @Neku42