Scala - 宏注释方法调用？

Question

我正在尝试编写一个简单的宏注释，它可以让我每次都为方法执行计时 - 如果我注释方法定义 - 或者如果我注释方法调用，则仅此一次。

注释方法定义工作得很好。不过

object Main {
  def main(args:Array[String]): Unit ={
    @MyMacro
    doTest() //"Hello World"
  }
}

似乎语法不正确。因为 intellij 抱怨在 :Unit ={ 之后它“期望”一个 }，当我删除 @MyMacro 时，一个警告就会消失。

注释方法调用（或任意表达式，就此而言）的正确方法是什么？

（例如，我可能对获取所有对 getX 的调用的时间不感兴趣，但我可能想在代码中的某个特定位置测量花费的时间：

val x = @MyMacro getX()

)

更新

这行得通：

object Main {
  def main(args:Array[String]): Unit ={
    hello()
  }

  @MyMacro
  def hello(): Unit ={
    println("Hello World")
  }
}

这不能编译：

object Main {
  def main(args:Array[String]): Unit ={
    hello(): @MyMacro
  }

  def hello(): Unit ={
    println("Hello World")
  }
}

因为

Error:(10, 15) macro annotation could not be expanded (the most common reason for that is that you need to enable the macro paradise plugin; another possibility is that you try to use macro annotation in the same compilation run that defines it)
hello(): @MyMacro
          ^

我只是用sbt 编译，使用

object BuildSettings {
  val buildSettings = Defaults.defaultSettings ++ Seq(
    version := "0.0.1",
    scalaVersion := "2.11.8",
    scalacOptions += "",
    crossScalaVersions := Seq("2.10.2", "2.10.3", "2.10.4", "2.10.5", "2.10.6", "2.11.0", "2.11.1", "2.11.2", "2.11.3", "2.11.4", "2.11.5", "2.11.6", "2.11.7", "2.11.8"),
    resolvers += Resolver.sonatypeRepo("releases"),
    addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)
  )
}

object ScalaMacroDebugBuild extends Build {
  import BuildSettings._

  lazy val root: Project = Project(
    "root",
    file("."),
    settings = buildSettings
  ) aggregate(macros, examples)

  lazy val macros: Project = Project(
    "macros",
    file("macros"),
    settings = buildSettings ++ Seq(
      libraryDependencies <+= (scalaVersion)("org.scala-lang" % "scala-compiler" % _))
  )

  lazy val examples: Project = Project(
    "examples",
    file("examples"),
    settings = buildSettings
  ) dependsOn(macros)
}

哪个应该同时解决这两个问题？

Answer 1

An annotation of an expression e appears after the expression e, separated by a colon.

所以val x = getX(): @MyMacro 应该可以工作。