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scala
dla programistów ruby :)
Tymon Tobolski
http://teamon.eu
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Scala - ???
• OOP + FP
• statycznie typowany
• kompilowany do JVM
• intergacja z Java
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scala jest trudna
trait FilterMonadic[+A, +Repr] {
def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That
// ...
}
def zipWithIndexIf[T](list: List[T])(pred: T => Boolean): List[(T, Option[Int])] = {
type R = List[(T, Option[Int])]
def doZip(zipped: R, left: List[T], index: Int): R = left match {
case x :: xs if pred(x) => doZip((x, Some(index)) :: zipped, xs, index + 1)
case x :: xs => doZip((x, None) :: zipped, xs, index)
case Nil => zipped
}
doZip(Nil, list, 0).reverse
}
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scala jest trudna
trait FilterMonadic[+A, +Repr] {
def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That
// ...
}
def zipWithIndexIf[T](list: List[T])(pred: T => Boolean): List[(T, Option[Int])] = {
type R = List[(T, Option[Int])]
def doZip(zipped: R, left: List[T], index: Int): R = left match {
case x :: xs if pred(x) => doZip((x, Some(index)) :: zipped, xs, index + 1)
case x :: xs => doZip((x, None) :: zipped, xs, index)
case Nil => zipped
}
doZip(Nil, list, 0).reverse
}
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serio?
List(1,2,3) map { e => e * 2 } // List[Int] = List(2, 4, 6)
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serio?
List(1,2,3) map { e => e * 2 } // List[Int] = List(2, 4, 6)
List(1,2,3) map (_*2) // List[Int] = List(2, 4, 6)
List(1,2,3) map (2*) // List[Int] = List(2, 4, 6)
List(1,2,3) filter { _ > 1 } // List[Int] = List(2, 3)
(1 to 10) foreach { e => println(e) }
(1 to 10) foreach println
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Monkey patching
2.days
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Monkey patching
Implicit
conversions
implicit def Int2Time(i: Int) = new {
def days = i * 24* 60 * 60
}
2.days // 172800
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Modules / Traits
module T1
def foo
"foo"
end
end
module T2
def bar
"bar"
end
end
class A
include T1
include T2
end
a = A.new
a.foo # => "foo"
a.bar # => "bar"
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Modules / Traits
trait T1 {
def foo = "foo"
}
trait T2 {
def bar = "bar"
}
class A extends T1 with T2
val a = new A
a.foo // "foo"
a.bar // "bar"
module T1
def foo
"foo"
end
end
module T2
def bar
"bar"
end
end
class A
include T1
include T2
end
a = A.new
a.foo # => "foo"
a.bar # => "bar"
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Singleton
class A
def foo
"instance"
end
class << self
def foo
"singleton"
end
end
end
A.new.foo # => "instance"
A.foo # => "singleton"
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Singleton
class A {
def foo = "instance"
}
object A {
def foo "singleton"
}
new A().foo // "instance"
A.foo // "singleton"
class A
def foo
"instance"
end
class << self
def foo
"singleton"
end
end
end
A.new.foo # => "instance"
A.foo # => "singleton"
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Duck typing
class Duck
def quack
def walk
end
class Dove
def quack
def walk
end
class Cat
end
def quack_and_walk(animal)
animal.quack
animal.walk
end
quack_and_walk Duck.new
quack_and_walk Dove.new
quack_and_walk Cat.new # NoMethodError
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Duck typing
class Duck {
def quack
def walk
}
class Dove {
def quack
def walk
}
class Cat
def quackAndWalk(a: { def quack; def walk }) = {
a.quack
a.walk
}
quackAndWalk(new Duck)
quackAndWalk(new Dove)
quackAndWalk(new Cat) // Compile error
class Duck
def quack
def walk
end
class Dove
def quack
def walk
end
class Cat
end
def quack_and_walk(animal)
animal.quack
animal.walk
end
quack_and_walk Duck.new
quack_and_walk Dove.new
quack_and_walk Cat.new # NoMethodError
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DSL
class StackSpec extends FlatSpec with ShouldMatchers {
"A Stack" should "pop values in last-in-first-out order" in {
val stack = new Stack[Int]
stack.push(1)
stack.push(2)
stack.pop() should equal (2)
stack.pop() should equal (1)
}
it should "throw NoSuchElementException if an empty stack is popped" in {
val emptyStack = new Stack[String]
evaluating { emptyStack.pop() } should produce [NoSuchElementException]
}
}
http://scalatest.org
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DSL
class FilterExample extends ScalatraFilter {
get("/hello") {
Hello world
} post("/world") { // ... } } https://github.com/scalatra/scalatraSlide 17
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Immutability
val list = List(2, 3)
val list2 = 1 :: list
println(list) // List(2, 3)
println(list2) // List(1, 2, 3)
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Built-in concurency
scala> (1 to 10) foreach println
1
2
3
4
5
6
7
8
9
10
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Built-in concurency
scala> (1 to 10).par foreach println
1
2
3
4
5
8
9
10
6
7
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
scala> Map(1 -> 2) get 1
res11: Option[Int] = Some(2)
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
scala> Map(1 -> 2) get 1
res11: Option[Int] = Some(2)
scala> Map(1 -> 2) get 3
res12: Option[Int] = None
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
scala> Map(1 -> 2) get 1
res11: Option[Int] = Some(2)
scala> Map(1 -> 2) get 3
res12: Option[Int] = None
scala> Map(1 -> 2) get 1 map (1+)
res13: Option[Int] = Some(3)
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
scala> Map(1 -> 2) get 1
res11: Option[Int] = Some(2)
scala> Map(1 -> 2) get 3
res12: Option[Int] = None
scala> Map(1 -> 2) get 1 map (1+)
res13: Option[Int] = Some(3)
scala> Map(1 -> 2) get 3 map (1+)
res14: Option[Int] = None
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
scala> Map(1 -> 2) get 1
res11: Option[Int] = Some(2)
scala> Map(1 -> 2) get 3
res12: Option[Int] = None
scala> Map(1 -> 2) get 1 map (1+)
res13: Option[Int] = Some(3)
scala> Map(1 -> 2) get 3 map (1+)
res14: Option[Int] = None
scala> Map(1 -> 2) get 1 map (1+) getOrElse 5
res15: Int = 3
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Functional style
scala> Map(1 -> 2)
res9: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2)
scala> Map(1 -> 2) get _
res10: (Int) => Option[Int] =
scala> Map(1 -> 2) get 1
res11: Option[Int] = Some(2)
scala> Map(1 -> 2) get 3
res12: Option[Int] = None
scala> Map(1 -> 2) get 1 map (1+)
res13: Option[Int] = Some(3)
scala> Map(1 -> 2) get 3 map (1+)
res14: Option[Int] = None
scala> Map(1 -> 2) get 1 map (1+) getOrElse 5
res15: Int = 3
scala> Map(1 -> 2) get 3 map (1+) getOrElse 5
res16: Int = 5
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Web
• Rails
• Sinatra
• ...
• Play!
• Lift
• Scalatra
• ...
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• Actors
• STM
• Fault Tolerance
• ...
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• http://scala-lang.org
• http://akka.io
• http://typesafe.com
• http://scala.playframework.org/
• #scala @ irc.freenode.net
• #scala.pl @ irc.freenode.net