Question

我想做与Scala Macros: Checking for a certain annotation类似的事情我的注释看起来像：

class extract(val name: String) extends StaticAnnotation

我正在使用它：

case class MainClass(@extract("strings") foo: String, bar: Int)

我正在尝试获取foo参数Symbol，因为它有一个@extract注释：

val extrList = params.map { param: Symbol =>
  param.annotations.collect {
    case extr if extr.tpe  <:< c.weakTypeOf[extract] =>
      val args = extr.scalaArgs
      if (args.size != 1)
        abort("@extract() should have exactly 1 parameter")
      getExtractValue(args.head) -> param
  }
}

getExtractValue方法如下所示：

def getExtractValue(tree: Tree): String = ???

如何获取name注释

的值@extract

更新

我从scalaArgs获得的树似乎无法被c.eval（）

使用

param: Symbol =>
    param.annotations.collect {
      case ann if ann.tpe <:< c.weakTypeOf[extract] =>
        val args = ann.scalaArgs
        val arg0 = args.head
        val name: String = c.eval(c.Expr(arg0))
        echo(s"args @extract(name = $name)")
        name -> param
    }

给出错误

[error] exception during macro expansion:
[error] scala.tools.reflect.ToolBoxError: reflective toolbox has failed: cannot
operate on trees that are already typed
[error]         at scala.tools.reflect.ToolBoxFactory$ToolBoxImpl$ToolBoxGlobal.
verify(ToolBoxFactory.scala:74)

完整的堆栈跟踪指向c.eval（我将c.eval与c.Expr分开）

Answer 1

在这种情况下：

def getExtractValue(tree: Tree) = tree match {
  case Literal(Constant(str: String)) => str
}

scala宏：如何读取注释对象

1 个答案: