I see that traits in Scala are similar to interfaces in Java (but interfaces in Java extend other interfaces, they don't extend a class). I saw an example on SO about traits usage where a trait extends a class.
What is the purpose of this? Why can traits extend classes?
If you read the answer you linked, you'll see that traits are very dissimilar to interfaces, since they can contain implementations.
You might also be interested in the difference between trait inheritance and self-type annotations: stackoverflow.com/questions/1990948/…
Yes, I understood the point that traits, unlike interfaces can contain partial implementation of methods, but I wasn't sure about the purpose of traits extending classes (as explained in the example)
T
Taky
Yes they can, a trait that extends a class puts a restriction on what classes can extend that trait - namely, all classes that mix-in that trait must extend that class.
scala> class Foo
defined class Foo
scala> trait FooTrait extends Foo
defined trait FooTrait
scala> val good = new Foo with FooTrait
good: Foo with FooTrait = $anon$1@773d3f62
scala> class Bar
defined class Bar
scala> val bad = new Bar with FooTrait
<console>:10: error: illegal inheritance; superclass Bar
is not a subclass of the superclass Foo
of the mixin trait FooTrait
val bad = new Bar with FooTrait
^
trait FooTrait { self:Foo => }. When would you use one technique versus the other?