class type error while working with generic method in scala

Question

Below is the code snippet...a bit testing mode code snippet.I am trying to create a method through which i can change the return type.

While calling the method i am getting the exception "class type expected object found"

trait A

trait B extends A {
  def aba[T](a:Int):T
}

class D

class C extends B {
  def aba[D](a:Int) = {
    println("asasas")
    new D
  }
}

dk14 · Accepted Answer · 2015-07-17 15:15:43Z

3

The actual error in Scala 2.11 is

:13: error: class type required but D found

Which means that you can't instantiate generic type D - your D class was shadowed by your [D] definition

You also can't override T (as a part of your aba's method signature) due to Liskov Substitution Principle as it will change behaviour (and signature) for subclass. However you can define T as type member:

trait A

trait B extends A {
  type T
  def aba(a:Int):T
}

class D 

class C extends B {
  type T = D
  def aba(a:Int): T = {
    println("asasas")
    new D
  }
}

answered Jul 17, 2015 at 15:15

dk14

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