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  1. abstract class Box[+T] {
  2.     def withFilter[A](p: T => Boolean) = if (isDefined && p(value)) {
  3.         println("Box.withFilter")
  4.         Full(value)
  5.     } else Empty
  6.  
  7.     def foreach(act: T => Unit) = if (isDefined) {
  8.         println("Box.foreach")
  9.         act(value)
  10.     }
  11.  
  12.     val isDefined: Boolean
  13.     def value: T
  14. }
  15. case object Empty extends Box[Nothing] {
  16.     override val isDefined = false
  17.     override def value = throw new RuntimeException("Empty box")
  18. }
  19. case class Full[T](item: T) extends Box[T] {
  20.     override val isDefined = true
  21.     override val value = item
  22. }
  23.  
  24. object Main extends App {
  25.     val empty = Empty
  26.     val full  = Full("Surprise")
  27.  
  28.     for (x <- empty) println("Empty :[")
  29.  
  30.     for {
  31.         x <- full
  32.         if x startsWith "Sur"
  33.         y <- Full(x.reverse)
  34.     } println(y)
  35. }
Success #stdin #stdout 0.3s 247488KB
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Standard input is empty
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Box.withFilter
Box.foreach
Box.foreach
esirpruS
https://ideone.com/kHZhDY
language:
Scala (scala 2.12.8)
created:
13 years ago
visibility:
public

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