scala - 如何在 Scala 中定义 @interface？

Question

如何在 Scala 中创建@interface？老实说，我觉得问这个问题很愚蠢，但我在任何地方都找不到这个语法。我知道您可以使用它们，但是如何在 Scala 中实际定义新的？

Java:

public @interface MyAnnotation { }

斯卡拉:

???

Answer 1

此答案基于 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

有关完整详细信息，请参阅 Scala Reference 中的第 11 节“用户定义的注释”例如，参见:@tailrec .

更新编译器警告说明了这一点:

>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

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