CODEWITHSUNDEEP
scalaprotectedtraits
Core_Dumped
Core_Dumped

Reputation: 4699

Is there any sense defining a variable as protected in a trait?

A trait cannot be instantiated. Hence, its fields can only be accessed by classes/traits/objects extending it. Hence, these two pieces of code are effectively the same:

trait foo{
    protected val fish:String
}
class bar extends foo{
    val fish = "catfish"
}

and 

trait foo{
    val fish:String
}
class bar extends foo{
    val fish = "catfish"
}

The protected access modifier is redundant for traits then. Right?

Upvotes: 0

Views: 930

Answers (1)

Ionuț G. Stan
Ionuț G. Stan

Reputation: 179119

It's redundant only because in the first version you've changed the visibility of the member from protected to public in the implementing class (by not marking it as protected). If you don't do that, then you can see that defining a member as protected in a trait means that a class has to implement it, but not expose it through its public API.

trait Foo {
  protected val fish: String
}

class Bar extends Foo {
  override protected val fish = "catfish"
}

val bar = new Bar
bar.fish // not visible

Upvotes: 4

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