CODEWITHSUNDEEP
scalainheritance
GrayR
GrayR

Reputation: 1385

Scala: overriding def with val

Consider following example:

abstract class Item {
  def price: Double
  def description: String
}

class SimpleItem1(override val price: Double, override val description: String) extends Item{}    
class SimpleItem2(val price: Double, val description: String) extends Item{}

It compiles successfully and both extended classes have same methods. Are they actually the same? If not - what is the difference? If yes - please explain this to me a little bit, for example: why they decided that 'override' is optional here?

Upvotes: 3

Views: 3936

Answers (1)

0__
0__

Reputation: 67290

Because price and description are abstract in Item, you are not required to use the override modifier. If they had default implementation, you would have to add the override modifier.

Thus, in SimpleItem1, the modifier is superfluous. There are some circumstances where adding an override "just in case" makes sense. For example if you define a trait that you might want to mix-in to a class that has a default implementation.

Here is an example, where override would make a difference:

trait Item0 {
  def price: Int
}

trait Item1 extends Item0 {
  def price = 33
}

trait Item2 extends Item0 {
  override def price = 33
}

object Foo1 extends Item1  // ok
object Foo2 extends Item2  // ok
object Foo3 extends Item0 with Item1  // ok
object Foo4 extends Item2 with Item1  // NOPE!
object Foo4 extends Item1 with Item2  // aha!

In general you should avoid using override where possible.

Upvotes: 10

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