Create instance of child from parent class

Question

I am building a simple DSL for length operations. I want the domain operations to be extensible, so I am using them as mixins along with the implicit conversions for my domain components.
1. Below is my App.

package com.shasank.funWithLengths

object LengthAdditionApp extends App{

  val length1 = 11 inches
  val length2 = 15 inches
  val length3 = 2 feet

  println(length1)
  println(length2)
  println(length3)
  println(length1 + length2) // all ok
  println(length1 + length3) // all ok
  println(length3 - length1) // all ok
  println(length1 + length2 + length2) // this breaks since object returned from first operation doesn't have adder

}

2. Below is my base class. I would have loved this to be abstract, but since I could not find a way to create instance of subclass Inches, I marked the constructor protected, so that only subclasses can extend it and nothing else can create an instance.

package com.shasank.funWithLengths

class Length protected(val measure: Int, val unit: String) {

  private def convertToInches(length: Length)= length.unit match {
    case "feet" => length.measure * 12
    case "inches" => length.measure
  }

  protected def operateOnMeasures(other: Length, op: (Int,Int) => Int): Length ={
    val thisInches = convertToInches(this)
    val otherInches = convertToInches(other)
    val operatedMeasure = op(thisInches,otherInches)
    new Length(operatedMeasure, "inches")  // object created does not have adder & subtracter capabilities
  }

  override def toString = {
    val measureInInches = convertToInches(this)
    val (feetMeasure, inchesMeasure) = BigInt(measureInInches) /% 12
    val feetMeasureString = s"$feetMeasure feet and"
    val inchesMeasureString = s"$inchesMeasure inches"
    s"$feetMeasureString $inchesMeasureString"
  }

}

3. Below are my domain components.

package com.shasank

package object funWithLengths {
  implicit class Inches(measure: Int) extends Length(measure, "inches") with Adder with Subtracter {
    def inches = this
  }
  implicit class Feet(measure: Int) extends Length(measure, "feet") with Adder with Subtracter {
    def feet = this
  }
}

4. Below are my domain operators.

package com.shasank.funWithLengths

trait Adder extends Length {
  def +(other: Length) = super.operateOnMeasures(other, _+_)
}

package com.shasank.funWithLengths

trait Subtracter extends Length {
  def -(other: Length) = super.operateOnMeasures(other, _-_)
}

Question: Is there a way to create an instance of Inches (so that I can get all the goodies of it) while returning from the method operateOnMeasures in my base class Length?

Answer 1

I was able to resolve this by moving the Length class inside the package object where I declared the implicit classes Inches and Feet.
Here is link to my working code