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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)
}
}
|
