Scala宏天堂: How do I get an annotation's arguments using macro annotations?

Question

假设我想使用宏注释来复制@specialized(Int) 之类的注释——我知道这很疯狂。像这样的东西:

class expand(expanded: Any*) extends Annotation with StaticAnnotation {
  def macroTransform(annottees: Any*) = macro expand.expandImpl
}

object expand {
 def expandImpl(c: Context)(annottees: c.Expr[Any]*):c.Expr[Any] = {        
    // would like to be able to get access to the "expanded" args above.
    ???
  }
}

// Usage:
 def foo[@expand(Int) T] = 4

有什么方法可以访问注释的参数(示例中的 Int)？

Answer 1

看看c.prefix。它将包含一个对应于 new expand(Int) 的树。

另一个选项是 c.macroApplication，它将是 new expand(Int).macroTransform(...)。