Question

Why if I have:

trait T {
  def method(a: Int)
}

class A extends T {
  //...
}

class B extends A {
  //...
}

then when I do this:

//...
val b = new B
b.method(15)
//...

the method() is said to be undefined for B? Why do I have to explicitly say that

class B extends A with T

in order to obtain what I want? Are not traits of parent classes inherited? How can it be so if they may realize a big part of parent’s own methods which are inherited by definition? If it is so, what is the argument?

Answer 1

I think you just did not implement the method method because I tested it on my computer and the following code works:

scala> trait T {
 | def method(a:Int) =a
 | }
defined trait T

scala> class A extends T
defined class A

scala> class B extends A
defined class B

scala> val b = new B
b: B = B@164a40a0

scala> b.method(11)
res25: Int = 11