如何创建注释，并让他们在斯卡拉 [英] How to create annotations and get them in scala

问题描述

我要定义一些注释和Scala中使用它们。

I want to define some annotations and use them in Scala.

我看着斯卡拉的来源， scala.annotation 包中发现，有喜欢的 tailrec 注释部分，开关， elidable ，等等。所以我定义了一些注解为他们做的：

I looked into the source of Scala, found in scala.annotation package, there are some annotations like tailrec, switch, elidable, and so on. So I defined some annotations as them do:

class A extends StaticAnnotation

@A
class X {
    @A
    def aa() {}
}

然后我写一个测试：

Then I write a test:

object Main {
    def main(args: Array[String]) {
        val x = new X
        println(x.getClass.getAnnotations.length)
        x.getClass.getAnnotations map { println }
    }
}

它打印一些奇怪的信息：

It prints some strange messages:

1
@scala.reflect.ScalaSignature(bytes=u1" !1* 1!AbCaE
9"a!Q!! 1gn!!.<b    iBPE*,7
    Ii#)1oY1mC&1'G.Y(cUGCa#=S:LGO/AA!A  1mI!)

我似乎不能得到注释 aaa.A 。

我怎样才能在斯卡拉创建注释是否正确？以及如何使用，让他们？

How can I create annotations in Scala correctly? And how to use and get them?

推荐答案

难道有事情做保留？我敢打赌，@tailrec不包括在如何产生的字节code。

Could it have something to do with retention? I bet @tailrec is not included in the bytecode getting generated.

如果我试图扩展ClassfileAnnotation（以有保留运行时），斯卡拉告诉我，它无法做到的，它有在Java中做：

If I try to extend ClassfileAnnotation (in order to have runtime retention), Scala tells me that it can't be done, and it has to be done in Java:

./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.
class A extends ClassfileAnnotation
      ^

这篇关于如何创建注释，并让他们在斯卡拉的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！