Scala self type annotation vs 'with' mix in

Question

Possible Duplicate:
What is the difference between scala self-types and trait subclasses?

I can't get the the difference between the two following code blocks:

    // Trait B is mixed in and creates a dependency on it
    trait A extends C with B { 
       ...
    }

    // Trait B is put in scope and also creates a dependency on it
    trait A extends C {
       self: B =>
    ...
    }

I'm asking from a design perspective.

Thanks!

Possibly the same as http://stackoverflow.com/questions/1990948/what-is-the-difference-between-scala-self-types-and-trait-subclasses — Ratan Sebastian, Jan 31 '13 at 19:09

score 4 · Accepted Answer · answered Jan 31 '13 at 19:21

4

When you use the self-type you constrain the trait to be used only when the specified self-type is satisfied by the other types with which it is mixed. You don't get an inheritance relationship between the trait being defined and the declared self-type. An implication of this is that the trait itself, as a static type in isolation, is not on its own publicly substitutable for the self-type. (It has been likened to C++ private inheritance, but it's a weak analogy).

answered Jan 31 '13 at 19:21

Randall Schulz

26,420
4
61
81

I've updated my example, I missed something. So in current case, do they provide the same design. – Jorge Olmos Jan 31 '13 at 19:31
@JorgeOlmos: I'm not sure what you mean by "provide the same design," but they certainly do not have the same semantics in Scala. – Randall Schulz Jan 31 '13 at 19:33
you're right, I was confused, Thanks! – Jorge Olmos Jan 31 '13 at 19:37

Scala self type annotation vs 'with' mix in

1 Answers1