Scala meetup - Milan, 25 May 2013 Una delle caratteristiche peculiari di Scala consiste nel semplificare e velocizzare la fase di sviluppo del software. Unificando la programmazione orientata agli oggetti con la programmazione funzionale, Scala permette di esprimervi in maniera concisa ed efficace. In questa presentazione saranno introdotte le caratteristiche principali del linguaggio e la sua filosofia, al fine di mostrare come del codice scritto in Scala risulti più semplice, corretto e manutenibile.

1. Scala
Simplifying Development
ScalaDay Italy
Milan, May 25, 2013
Mirco Dotta
Sunday, May 26, 13

2. Is Scala the Java of the
future?
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3. • It has basically everything Java has now
• It has closures (planned for Java 8)
• It has rich interfaces (Java 8 defender
methods), and more
• It is completely interoperable and runs
about as fast as Java
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4. How is Scala different
from Java?
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5. Concise Syntax
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6. public class Time {
private final int hours;
private final int minutes;
public Time(int hours, int minutes) {
this.hours = hours;
this.minutes = minutes;
}
public int getHours() { return hours; }
public int getMinutes() { return minutes; }
}
class Time(val hours: Int, val minutes: Int)
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7. Statically typed
but feels dynamic
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8. val x = 2
type is inferred
no semicolon
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9. Unifies OOP and FP
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10. Every value is an object
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11. List(1,2,3).filter(x => x > 2) //> res: List[Int] = List(3)
Anonymous function Int => Boolean
List(1, 2, 3).filter(
new Function[Int, Boolean] {
def apply(x: Int): Boolean = x > 2
}
)
/
//> res: List[Int] = List(3)
Functions are “just” objects
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12. Everything is an
expression
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13. def max(x: Int, y: Int): Int =
if (x > y) x else y
no return statement
val x: Int = {
val y = 10
val z = 5
y + z
}
blocks evaluate to last
expression
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14. Every operation is a
method call
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15. val x: Int = 10
val y = x + 10
same as x.+(10)
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16. Principles, not Rules
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17. Users can write their own operators
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Principle
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18. class Complex(val re: Int, val im: Int = 0) {
def +(that: Complex) =
new Complex(this.re + that.re, this.im + that.im)
override def toString = s"$re + $im"
}
val c1 = new Complex(1, 2) //> c1 : Complex = 1 + 2
val c2 = new Complex(2, 2) //> c2 : Complex = 2 + 2
val c = c1 + c2 //> c : Complex = 3 + 4
default argument
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19. • new types can look like built-in ones
• “grow the language”
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20. Powerful collections
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21. case class Time(hours: Int, minutes: Int = 0)
val times = List(Time(1), Time(2), Time(12,30), Time(16,15))
times.filter(time => time.hours >= 12)
//> res: List[Time] = List(Time(12,30), Time(16,15))
times.map(time => Time(time.hours + 1, time.minutes))
//> res: List[Time] = List(Time(2,0), Time(3,0), Time(13,30),
Time(17,15))
times.take(2) //> res: List[Time] = List(Time(1,0), Time(2,0))
times.groupBy(time => time.minutes) //> res: Map[Int,List[Time]] =
Map(30 -> List(Time(12,30)), 15 -> List(Time(16,15)), 0 ->
List(Time(1,0), Time(2,0)))
times.head //> res: Time = Time(1,0)
times.last //> res: Time = Time(16,15)
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22. For-comprehension
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23. • More general than for-loops
• Used to iterate, filter, and generate new
collections
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24. for (p <- persons; pr <- p.projects;
if pr.overdue) yield p.name
may have any number of generators
guard construct a new collection of the same
type, element by element
p is in scope for other generators
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25. times.filter(time => time.hours >= 12)
//> res: List[Time] = List(Time(12,30), Time(16,15))
for(time <- times;
if time.hours >= 12) yield time
//>res: List[Time] = List(Time(12,30), Time(16,15))
times.map(time => Time(time.hours + 1, time.minutes))
//> res: List[Time] = List(Time(2,0), Time(3,0), Time(13,30),
Time(17,15))
for(time <- times)
yield Time(time.hours + 1, time.minutes)
//> res: List[Time] = List(Time(2,0), Time(3,0), Time(13,30),
Time(17,15))
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26. Desugared to calls to filter, map, and
flatMap
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27. Readily available on any class
implementing those methods!
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28. Traits
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29. • Like Java interfaces, but traits
• can have behavior (like Java 8 interfaces
with defender methods)
• can have state
• enable multiple inheritance
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30. public interface Comparable<T> {
int compareTo(int o);
}
trait Comparable[T] {
def compareTo(that: T): Int
}
def <(that: T): Boolean =
(this compare that) < 0
def >(that: T): Boolean =
(this compare that) > 0
//... Rich
Interface
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31. Multiple Inheritance
• Traits can mix-in multiple traits
• Classes can mix-in multiple traits
• Both Class and Trait can inherit at most
from one Class
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32. trait Bird {
def fly: String = "I'm flying!"
}
trait Swimmer {
def swim: String = "I'm swimming!"
}
class Fish extends Swimmer
class Duck extends Bird with Swimmer
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33. Embedding DSLs
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34. Scala simplifies
development because...
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35. Less is More
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36. Few language
constructs with high
abstraction power
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37. It’s Fun!
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38. Good for your
business?
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39. 37/38
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40. Get Started in 5’
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http://www.typesafe.com/platform/getstarted
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41. Thanks
twitter: @mircodotta
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