Extend trait with private constructor parameter

Question

In Scala, how can I extend a trait in a class with private constructor parameter that is defined in the trait?

trait Parent {
  protected def name: String
  require(name != "", "wooo problem!")
}

class Child(private val name: String) extends Parent {
  println("name is " + name)
}

The above class gives an error:

class Child needs to be abstract, since method name in trait Parent of type ⇒ String is not defined.

Of-course I can:

1. make the Child class abstract,
2. define it without using the private in the constructor like class Child(val name: String).
3. make the Parent an abstract class instead of a trait

But with the above implementation, is there no way I can have a private constructor parameter while extending a trait? Note that I want the variable to be private so that I should not be able to do childInstance.name.

Answer 1

Try this

  trait Parent {
    protected def name: String
    require(name != "", "wooo problem!")
  }

  class Child(override protected val name: String) extends Parent {
    val publicVar = "Hello World"
    println("name is " + name)
  }

  def main(args: Array[String]): Unit = {
    val child = new Child("John Doe")
    println(child.publicVar)
    println(child.name) // Does not compile
  }

You will not be able to access to child.name