How to define an assignment operator in Scala?

Question

For example, I have defined a +* operator for weighted sum in the following wrapper class for Double:

  class DoubleOps(val double: Double) {
    def +*(other: DoubleOps, weight: Double): DoubleOps =
      new DoubleOps(this.double + other.double * weight)
  }

  object DoubleOps {
    implicit def DoubleToDoubleOps(double: Double) = new DoubleOps(double)
  }

With this definition, I can have the following calculation:

var db: DoubleOps = 1.5
import DoubleOps._
db = db +* (2.0, 0.5)
println(db)

Is there a way I can calculate db using an assignment operator to get the result, like to define a +*=, so that I can use:

db +*= (2.0, 0.5)

Is this possible?

sarveshseri · Accepted Answer · 2018-01-22 07:29:43Z

4

import scala.languageFeature.implicitConversions

class DoubleOps(var double: Double) {
  def +*(other: DoubleOps, weight: Double): DoubleOps =
    new DoubleOps(this.double + other.double * weight)

  def +*=(other: DoubleOps, weight: Double): Unit = {
    this.double = this.double + other.double * weight
  }
}

object DoubleOps {
  implicit def DoubleToDoubleOps(double: Double) = new DoubleOps(double)
}

val d: DoubleOps = 1.5

d +*= (2.0, 0.5)

answered Jan 22, 2018 at 7:29

sarveshseri

14k30 silver badges50 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Fried Brice Over a year ago

We all should take this as an opportunity to meditate on the distinction between reassignment and mutation.

sarveshseri Over a year ago

Yes that is one subtlety. The OP wants mutation but he wrote assignment.

Fried Brice Over a year ago

Right, reassignment cannot be a method AFAIK because it doesn't change something within the object, it changes something in the environment.

CyberPlayerOne Over a year ago

It's because in the book "Scala for the impatient" the author calls it "assignment operator".

Fried Brice Over a year ago

@Tyler提督九门步军巡捕五营统领 I see. I think I remember that part of the book.

Collectives™ on Stack Overflow

How to define an assignment operator in Scala?

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related