Scala example source code file (builders.scala)

This example Scala source code file (builders.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

a, b, b, builder, c, d, d, elem, iter, iterable, iterable, list, list, to

The Scala builders.scala source code

object builders {

  trait Builder[-From, +To, -Elem] {
    def += (elem: Elem)
    def result: To
  }

  implicit def iterableBuilder[A, B] = new Builder[Iterable[A], Iterable[B], B] {
    println("new iterable builder")
    private val buf = new scala.collection.mutable.ListBuffer[B]
    def += (elem: B) { buf += elem }
    def result: Iterable[B] = buf.toList
  }

  implicit def listBuilder[A, B] = new Builder[List[A], List[B], B] {
    println("new list builder")
    private val buf = new scala.collection.mutable.ListBuffer[B]
    def += (elem: B) { buf += elem }
    def result: List[B] = buf.toList
  }
/*  
  def fill[A, Dim1, Dim2, Coll](n1: Int, n2: Int, elem: A)(implicit b1: Builder[Coll, Dim1, A], b2: Builder[Coll, Dim2, Dim1]) = {
    for (i <- 0 until n1) {
      for (j <- 0 until n2) {
        b1 += elem
      }	
      b2 += b1.result
    }
    b2.result
  }	
*/
/*
  implicit def arrayBuilder[A, B] = new Builder[Array[A], Array[B], B] {
    println("new arr ay builder")
    private val buf = new scala.collection.mutable.ListBuffer[B]
    def += (elem: B) { buf += elem }
    def result: Array[B] = buf.toArray
  }	
*/
  class Iter[A, C](elems: List[A]) {
    def ++ [B  >: A, D](xs: Iterable[B])(implicit b: Builder[C, D, B]): D = {
      for (x <- elems) b += x
      for (x <- xs) b += x
      b.result
    }
    def map[B, D](f: A => B)(implicit b: Builder[C, D, B]): D = {
      for (x <- elems) b += f(x)
      b.result
    }
  }
  
  def main(args : Array[String]) : Unit = {
    val x1 = new Iter[Int, List[Int]](List(1, 2, 3))
//    val x2 = new Iter[Int, Array[Int]](List(1, 2, 3))
    val x3 = new Iter[Int, Iterable[Int]](List(1, 2, 3))
    val y1: List[Int] = x1.map (_ + 1)
//    val y2: Array[Int] = x2.map (_ + 1)
    val y3: Iterable[Int] = x3.map (_ + 1)
    val z1: List[Int] = y1
//    val z2: Array[Int] = y2
    val z3: Iterable[Int] = y3
    println(z1)
//    println(z2)
    println(z3)
  }
}