如何在Scala中定義@interface？

Question

如何在Scala中創建一個@interface？我誠實地感到愚蠢的問這個問題，但我找不到任何地方的語法。我知道你可以使用它們，但是你怎麼在Scala中定義新的？

的Java：

public @interface MyAnnotation { } 

斯卡拉：

??? 

Answer 1

這個答案是基於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 

有關詳情，請參閱第11的Scala Reference 見 「用戶定義的註釋」，例如：@tailrec。

UPDATE編譯器警告最好說它：

>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

如果你想創建斯卡拉你應該混合StaticAnnotation或ClassAnnotation性狀的註釋。示例代碼：

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