具有通用类型的Scala重载运算符

Question

I am doing a project in scala and i am struggling with a certain thing. I am making a matrix DSL so i am overloading some operators like +,- or * so that i can do :

matrixMult = matrix1*matrix2

The thing is i made this class where the matrix was represented as a Array[Array[Double]] type but i would like to make it generic: Array[Array[T]]

The thing is i do not know how to handle this in the class methods since for operations like +,- and *. It should work for doubles or ints, but strings should throw an error. Here is my current code:

  def +(other : Matrix[Double]): Matrix[Double] = {
  var array = new Array[Array[Double]](rows)
  for (i <- 0 to (rows - 1)) {
    var arrayRow = new Array[Double](columns)
    for (j <- 0 to (columns - 1)) {
      arrayRow(j) = this.array(i)(j) + other.array(i)(j)
    }
    array(i) = arrayRow
  }
  return new Matrix(array)

}

I get an error on the arrayRow(j) =... line which is normal because it does not know what type the "this" object is. What should i do to make this work? Like i would like this method only to be accessible to doubles (or ints) and not strings, if this method was to be invoked on a Matrix[String] object it should throw an error. I tried pattern matching with isInstanceOf() but that doesn't remove the error and i can't compile.

If kind of have the same issue with all of my methods in my class, so i'd like a generic answer if possible.

Any help is appreciated, Thank you very much!

Answer 1

Not sure which version of Scala you are using, but if you're on 2.8, I found this thread on Scala-lang, and it looks like you may be able to use T:Numerics to limit it to Int, Long, Float, Double.

A little farther down in the thread, to limit it to JUST a subset of those (like Int, Double), they say to define your own generic Trait. https://www.scala-lang.org/old/node/4787

Answer 2

Answer can be found in comments:

Matrix addition has been asked, and answered, before. Even though the question posses a different matrix implementation, I believe the answer from the redoubtable Rex Kerr is still applicable. – jwvh