Section 5.1 talks about "with ScalaObject" being added implicitly. This may be confusing as mentioning  "with ScalaObject" explicitly, as in the example code below, leads to compile errors:-


Example 5.1.3  (without the "..." )
abstract class AbsIterator extends AnyRef with ScalaObject {  }

The code is rejected by the compiler:-

:30: error: trait ScalaObject is inherited twice
abstract class AbsIterator extends AnyRef with ScalaObject {  }
                                               ^
:30: error: trait ScalaObject is inherited twice
abstract class AbsIterator extends AnyRef with ScalaObject {  }
                           ^
two errors found



"
Example 5.1.6 Consider the class definitions
class A { def f: Int = 1 ; def g: Int = 2 ; def h: Int = 3 }
abstract class B { def f: Int = 4 ; def g: Int }
abstract class C extends A with B { def h: Int }
"

"trait B" is needed instead of "abstract class B"

The current code is rejected by the compiler:-

error: class B needs to be a trait be mixed in
abstract class C extends A with B { def h: Int }
                                ^
one error found