"macro implementation reference has wrong shape" Scala 文档示例中的内容

Question

以下宏是从http://docs.scala-lang.org/overviews/quasiquotes/usecases.html:

粘贴过来的

import reflect.macros.Context
import language.experimental.macros
val universe = reflect.runtime.universe; import universe._
import reflect.runtime.currentMirror
import tools.reflect.ToolBox
val toolbox = currentMirror.mkToolBox()
object debug {
  def apply[T](x: =>T): T = macro impl
  def impl(c: Context)(x: c.Tree) = { import c.universe._
    val q"..$stats" = x
    val loggedStats = stats.flatMap { stat =>
      val msg = "executing " + showCode(stat)
      List(q"println($msg)", stat)
    }
    q"..$loggedStats"
  }
}

在Scala 2.11.1中产生如下错误信息:

Q.scala:9: error: macro implementation reference has wrong shape. required:
macro [<static object>].<method name>[[<type args>]] or
macro [<macro bundle>].<method name>[[<type args>]]
  def apply[T](x: =>T): T = macro impl
                                  ^

我尝试过以多种方式改变代码(import reflect.macros.whitebox.Context, import reflect.macros.blackbox.Context，将scala.放在每次导入的开始，使参数一致地按名称或一致地按值，macro impl[T]，摆脱类型参数，macro debug.impl，将apply放在impl之后，等等)，但没有成功。我做错了什么?是进口的问题吗?这些(大部分)来自一个不同的网页，http://docs.scala-lang.org/overviews/quasiquotes/setup.html。

同样的错误出现在该页的其他两个示例宏上:

object Macro {
  def apply(x: Int): Int = macro impl
  def impl(c: Context)(x: c.Expr[Int]): c.Expr[Int] = { import c.universe._
    c.Expr(q"$x + 1")
  }
}
object Macro {
  def apply(x: Int): Int = macro impl
  def impl(c: Context)(x: c.Tree) = { import c.universe._
    q"$x + 1"
  }
}

Answer 1

scala Foo.scala将您提供给它的代码包装在一个匿名类中。因此，类似于:

import scala.reflect.macros.Context
import scala.language.experimental.macros
object debug {
  def apply[T](x: T): T = macro impl
  def impl(c: Context)(x: c.Tree): c.Tree = ???
}

转换成:

[[syntax trees at end of                    parser]] // Test.scala
package <empty> {
  object Main extends scala.AnyRef {
    def <init>() = {
      super.<init>();
      ()
    };
    def main(args: Array[String]): scala.Unit = {
      final class $anon extends scala.AnyRef {
        def <init>() = {
          super.<init>();
          ()
        };
        import scala.reflect.macros.Context;
        import scala.language.experimental.macros;
        object debug extends scala.AnyRef {
          def <init>() = {
            super.<init>();
            ()
          };
          <macro> def apply[T](x: T): T = impl;
          def impl(c: Context)(x: c.Tree): c.Tree = $qmark$qmark$qmark
        }
      };
      new $anon()
    }
  }
}

但是，宏实现必须在静态对象或捆绑包中定义，这就是错误消息试图说的:

/Users/xeno_by/Projects/211x/sandbox/Test.scala:5: error: macro implementation reference has wrong shape. required:
macro [<static object>].<method name>[[<type args>]] or
macro [<macro bundle>].<method name>[[<type args>]]
  def apply[T](x: T): T = macro impl
                                ^
one error found

不幸的是，如果将某些东西放入匿名类中，它就不再是静态的，这意味着scala Foo.scala风格的开发与宏不兼容。请考虑使用其他选项，例如scalac或sbt。