你如何在 Scala 中定义@interface? [英] How do you define an @interface in Scala?

问题描述

如何在 Scala 中创建 @interface?老实说，我觉得问这个问题很愚蠢，但我找不到这个 anywhere 的语法.我知道你可以使用它们，但你如何在 Scala 中实际定义新的?

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 { }

斯卡拉:

???

推荐答案

这个答案基于 Scala 2.8.

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

有关详细信息，请参阅 Scala 参考参见，例如:@tailrec.

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

更新编译器警告说得最好:

>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

讨论

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