Question

我开始在Scala中搞乱泛型，这是一个难以破解的cookie。我的想法是通过编写一个通用矩阵类来学习它，以便在我的并行计算项目中使用。

但是，在实例化新矩阵时我无法使用Array.fill（）。这是我的Matrix代码：

（小心砖墙）

package dm8xx.matrix.immutable
import scala.util.Random

/*
 * Bring your sunglasses...
 */

object Matrix {
  def apply[T](m: Int, n: Int, v: T )(implicit nn:Numeric[T],mm:ClassManifest[T]): Matrix[T] = {
    println("making new mat")
    println(mm)
      new Matrix[T](Array.fill(m,n)(v))
  }
  def apply[T: Numeric](m: Int, n: Int): Matrix[T] = Matrix(m, n)
  def apply(m: Int, n: Int, r: Random): Matrix[Double] =
    new Matrix(Array.fill[Double](m, n) { Math.floor(r.nextDouble() * 100) })

}

class Matrix[T: Numeric](val data: Array[Array[T]]) {
  val num = implicitly[Numeric[T]]
  implicit val cm: ClassManifest[T] = implicitly
  val m = data.size
  val n = data(0).size
  def apply(i: Int, j: Int) = data(i)(j)

  def map(f:T=>T)= new Matrix(data.map(_.map(f)))

  def pieceWise(f: (T, T) => T, that: Matrix[T]): Matrix[T] = {
    val temp: Array[Array[T]] = Array.ofDim[T](m, n)
    for (i <- 0 until m; j <- 0 until n) temp(i)(j) = f(data(i)(j), that.data(i)(j))
    return new Matrix(temp)
  }
  def +(that: Matrix[T]) = pieceWise(num.plus(_, _), that)
  def -(that: Matrix[T]) = pieceWise(num.minus(_, _), that)
  def *(that: Matrix[T]) = {
    val temp = Matrix[T](m,that.n,num.one)
    for (i <- 0 until m; j <- 0 until n; k <- 0 until that.n)
      temp.data(i)(k) = num.plus(temp.data(i)(k) , num.times( data(i)(j) , that.data(j)(k)))
    temp
  }

  override def toString() = (for (i <- 0 until m) yield "\n" + (for (j <- 0 until n) yield data(i)(j))).toString

}

一切都在编译，我甚至可以运行我的测试，但它在某个时刻失败了。我正在运行的测试如下：

  val M = 100
  val N = 100
  val threads = false
  def main(args: Array[String]) {
    val r = new Random(2)
    val a: Matrix[Double] = Matrix(M, N, r)
    val b: Matrix[Double] = Matrix(N, M, r)
    println(a)
    println(b)
    var m12 = a * b
  }

此操作失败，但出现以下异常：

Exception in thread "main" scala.MatchError: null
    at scala.reflect.ClassManifest$.arrayType(ClassManifest.scala:206)
    at scala.Array$.fill(Array.scala:254)
    at dm8xx.matrix.immutable.Matrix$.apply(Matrix.scala:12)
    at dm8xx.matrix.immutable.Matrix.$times(Matrix.scala:37)
    at dm8xx.matrix.MatrixTest$.main(MatrixTest.scala:19)
    at dm8xx.matrix.MatrixTest.main(MatrixTest.scala)

有人能告诉我为什么班级清单在此时为空吗？很抱歉放了这么多代码，但我无法确定我的错误所在，所以我必须报告所有内容。（当我得到一个好的答案时，也许我可以删除无关紧要的部分。）

好的，现在代码可以运行，但当然它比使用Double的直接实现慢了至少10倍......这就是最终矩阵的样子（如果有人有兴趣的话）：

package dm8xx.matrix.immutable
import scala.util.Random

/*
 * Bring your sunglasses...
 */

object Matrix {
  def apply[T](m: Int, n: Int, v: T)(implicit nn: Numeric[T], mm: ClassManifest[T]): Matrix[T] = {
    new Matrix[T](Array.fill(m, n)(v))
  }
  def apply[T](m: Int, n: Int)(implicit num: Numeric[T], cm: ClassManifest[T]): Matrix[T] = Matrix[T](m, n, num.zero)
  def apply(m: Int, n: Int, r: Random): Matrix[Double] =
    new Matrix(Array.fill[Double](m, n) { Math.floor(r.nextDouble() * 100) })
}

class Matrix[T: Numeric: ClassManifest](val data: Array[Array[T]]) {
  val num = implicitly[Numeric[T]]
  val cm: ClassManifest[T] = implicitly
  val m = data.size
  val n = data(0).size
  def apply(i: Int, j: Int) = data(i)(j)

  def map(f: T => T) = new Matrix(data.map(_.map(f)))

  def pieceWise(f: (T, T) => T, that: Matrix[T]): Matrix[T] = {
    val temp: Array[Array[T]] = Array.ofDim[T](m, n)
    for (i <- 0 until m; j <- 0 until n) temp(i)(j) = f(data(i)(j), that.data(i)(j))
    return new Matrix(temp)
  }
  def +(that: Matrix[T]) = pieceWise(num.plus(_, _), that)
  def -(that: Matrix[T]) = pieceWise(num.minus(_, _), that)
  def *(that: Matrix[T]) = {
    val temp = Matrix[T](m, that.n, num.zero)
    for (i <- 0 until m; j <- 0 until n; k <- 0 until that.n)
      temp.data(i)(k) = num.plus(temp.data(i)(k), num.times(data(i)(j), that.data(j)(k)))
    temp
  }

  override def toString() = (for (i <- 0 until m) yield "\n" + (for (j <- 0 until n) yield data(i)(j))).toString

}

Answer 1

这似乎有效：

class Matrix[T: Numeric: ClassManifest](val data: Array[Array[T]]) {
  val num = implicitly[Numeric[T]]
  val cm: ClassManifest[T] = implicitly
...

Answer 2

尝试使用Manifest代替ClassManifest

当包含基元时，数组需要额外的处理，因为它们是有效的，但是ClassManifest旨在用于类（名称是赠品）

Scala隐式ClassManifest [T]在Array.fill（..）中为null

2 个答案: