How do you define an @interface in Scala?

Question

How does one create an @interface in Scala? I honestly feel stupid asking that question, but I can't find the syntax for this anywhere. I know that you can consume them, but how do you actually define new ones in Scala?

Java:

public @interface MyAnnotation { }

Scala:

???

Answer 1

This answer is based on Scala 2.8.

// Will be visible to the Scala compiler, but not in the class file nor at runtime.
// Like RetentionPolicy.SOURCE
final class MyAnnotation extends StaticAnnotation

// Will be visible stored in the annotated class, but not retained at runtime.
// This is an implementation restriction, the design is supposed to support
// RetentionPolicy.RUNTIME
final class MyAnnotation extends ClassfileAnnotation

For the full details, see section 11 "User Defined Annotations" in the Scala Reference See, for example: @tailrec.

UPDATE The compiler warning says it best:

>cat test.scala
final class MyAnnotation extends scala.ClassfileAnnotation

@MyAnnotation
class Bar

>scalac test.scala
test.scala:1: warning: implementation restriction: subclassing Classfile does not
make your annotation visible at runtime.  If that is what
you want, you must write the annotation class in Java.
final class MyAnnotation extends scala.ClassfileAnnotation

Discussion

Answer 2

If you want to create an annotation in Scala you should mix StaticAnnotation or ClassAnnotation traits. Example code:

class MyBaseClass  {}  
class MyAnnotation(val p:String) extends MyBaseClass with StaticAnnotation  {}
@MyAnnotation("AAA")  
class MyClass{}