如何在Scala中定义@interface？

Question

如何在Scala中创建一个@interface？我诚实地感到愚蠢的问这个问题，但我找不到任何地方的语法。我知道你可以使用它们，但是你怎么在Scala中定义新的？

的Java：

public @interface MyAnnotation { } 

斯卡拉：

??? 

Answer 1

这个答案是基于Scala的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 

有关详情，请参阅第11的Scala Reference 见 “用户定义的注释”，例如：@tailrec。

UPDATE编译器警告最好说它：

>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

如果你想创建斯卡拉你应该混合StaticAnnotation或ClassAnnotation性状的注释。示例代码：

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