Question

could you explain me what is incorrect in this trivial example?

class C1 (val id: Int) 

abstract class C2 [T] {
    def m1 [T] 
}

class C3 [C1] extends C2
{
    override 
    def m1 (obj: C1) {
        println (obj.id)        
    }           
}

I have got: value id is not a member of type parameter C1
Why?

Answer 1

There is several things at play in your example. Here is the example modified:

class C1 (val id: Int) 

abstract class C2 [T] {
  // don't repeat [T] and the method takes an arg
  // within C2, T refers to the type parameter
  def m1(t:T) 
}

class C3 extends C2[C1] {  // if in REPL put the brace on the same line
  // no override when implementing abstract 
  def m1(obj:C1) { println(obj.id) } 
}

This should compile (and run in the REPL).