如何在 Scala 中定义和使用自定义注解 [英] How to define and use custom annotations in Scala

问题描述

我正在尝试在 Scala 中使用自定义注释.在此示例中，我创建了一个要使用元数据进行注释的字符串(在本例中为另一个字符串).然后，给定一个数据实例，我想读取注释.

I am trying use a custom annotation in Scala. In this example, I create a string that I want to annotate with metadata (in this case, another string). Then, given an instance of the data, and I want to read the annotation.

scala> case class named(name: String) extends scala.annotation.StaticAnnotation
defined class named

scala> @named("Greeting") val v = "Hello"
v: String = Hello

scala> def valueToName(x: String): String = ???
valueToName: (x: String)String

scala> valueToName(v) // returns "Greeting" 

这甚至可能吗?

推荐答案

使用 Scala 2.11.6，这可以提取注释的值:

With scala 2.11.6, this works to extract values of a annotation:

case class Named(name: String) extends scala.annotation.StaticAnnotation

val myAnnotatedClass: ClassSymbol = u.runtimeMirror(Thread.currentThread().getContextClassLoader).staticClass("MyAnnotatedClass")
val annotation: Option[Annotation] = myAnnotatedClass.annotations.find(_.tree.tpe =:= u.typeOf[Named])
val result = annotation.flatMap { a =>
  a.tree.children.tail.collect({ case Literal(Constant(name: String)) => doSomething(name) }).headOption
}

这篇关于如何在 Scala 中定义和使用自定义注解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！