Aşağıdaki kod derlenmiş başarısız olur, ancak ek açıklamasını dot
yönteminde kaldırırsam iletilir.Bu scala'nın uzmanı bir böcek mi?
Scala kod koşucu versiyonu 2.12.0-RC2 - Telif Hakkı 2002-2016, LAMBA/epfl ve Lightbend, Inc
abstract class Op[@specialized Left, @specialized Right] {
@specialized
type Result
def r: Numeric[Result]
def times(left: Left, right: Right): Result
}
object Op {
implicit object IntDoubleOp extends Op[Int, Double] {
type Result = Double
val r = implicitly[Numeric[Double]]
def times(left: Int, right: Double): Double = left * right
}
}
object calc {
def dot[@specialized Left, @specialized Right](xs: Array[Left], ys: Array[Right])
(implicit op: Op[Left, Right]): op.Result = {
var total = op.r.zero
var index = xs.length
while(index > 0) {
index -= 1
total = op.r.plus(total, op.times(xs(index), ys(index)))
}
total
}
}
test.scala:31: error: type mismatch;
found : op.Result
required: op.Result
total
^
one error found
İşte
başka hiçbir şans ile deneyin:
//cat Ops.scala
import scala.{ specialized => sp }
trait OpsResult {
type N
}
trait SymOps extends OpsResult {
@sp override type N
def zero: N
def plus(left: N, right: N): N
}
trait AsyOps[@sp L, @sp R] extends OpsResult {
@sp override type N
def times(left: L, right: R): N
}
trait MixOps[@sp L, @sp R] extends AsyOps[L, R] with SymOps
object MixOps {
trait DoubleOps extends SymOps {
override type N = Double
def zero: Double = 0.0
override def plus(left: Double, right: Double): Double = left + right
}
trait IntDoubleOps extends AsyOps[Int, Double] {
override type N = Double
override def times(left: Int, right: Double): Double = left * right
}
implicit object MixIntDouble extends IntDoubleOps with DoubleOps
}
object Test {
def dot[@sp L, @sp R](xs: Array[L], ys: Array[R])
(implicit op: MixOps[L, R]): op.N = {
op.zero
}
}
$ scalac Ops.scala
Ops.scala:36: error: type mismatch;
found : op.N
required: op.N
op.zero
^
one error found