定义其他特征的Scala特征

Question

I ran into an interesting scenario in Scala. It seems then I have a base trait that defines other traits, the implementation cannot find the base trait not matter what.

I created this base trait simple for convenience that I don't need to redefined these traits on every implementation. Do anyone know why this doesn't work?

object Base {
   trait Create
   trait Delete
}

trait BaseTrait {
   trait Create extends Base.Create
   trait Delete extends Base.Delete
}

object Implementation extends BaseTrait 

object Something {
   class SomeClass extends Implementation.Create //The trait is not defined. 
}

Update:
The question has been cleared up a bit so that its more precise. The solution as @BrianHsu pointed out is that trait cannot be inherited.

Answer 1

This block of code is fine:

object Base {
  trait Event
  trait Command
}

The following block will run into to trouble:

trait BaseTrait {
  trait Event extends Event
  trait Command extends Command
}

But Scala compiler says it very clearly.

test.scala:7: error: illegal cyclic reference involving trait Event
  trait Event extends Event
              ^
test.scala:8: error: illegal cyclic reference involving trait Command
  trait Command extends Command

Of course you cannot do this, just like you could not do the following in Java:

class HelloWorld extends HelloWorld

You have to specify that what you extend is actually Base.Event / Base.Command, so it will only work if you write it as:

trait BaseTrait {
  trait Event extends Base.Event
  trait Command extends Base.Command
}

Another problem in your code it the last Something object, it does not make sense at all:

object Something {
  Implementation.Event
  Implementation.Commannd
}

So compiler give you a clear error message:

test.scala:14: error: value Event is not a member of object Implementation
  Implementation.Event
                 ^
test.scala:15: error: value Commannd is not a member of object Implementation
  Implementation.Commannd

It's quite obvious, an trait in Scala is much like interface in Java, you should not use it as it is a field.