Question

  trait App extends DelayedInit {
  //...
  private val initCode = new ListBuffer[() => Unit]

  /** The init hook. This saves all initialization code for execution within `main`.
   *  This method is normally never called directly from user code.
   *  Instead it is called as compiler-generated code for those classes and objects
   *  (but not traits) that inherit from the `DelayedInit` trait and that do not
   *  themselves define a `delayedInit` method.
   *  @param body the initialization code to be stored for later execution
   */
  override def delayedInit(body: => Unit) {
    initCode += (() => body)
  }
  //...
}

object CircuitMain extends App {
  // You can write tests either here, or better in the test class CircuitSuite.
  Circuit.andGateExample //line in question ?
}

Related Post why-if-i-extend-the-app-trait-in-scala -i-override-the-main-method

我可以看到在评论中它说它将由编译器生成的代码调用从相关帖子中可以看出，scala编译器会对 DelayedInit 做一些特殊的事情，是什么让这个 DelayedInit 特性如此特别？它是语言相关的功能吗？或者我们也可以对其他特征做类似的事情？如果是，那该怎么做。

Answer 1

前几天我在琢磨这个......

是的，这是一种特定于语言的功能 - 请参阅Scala语言规范中的第5.1节“延迟初始化”： http://www.scala-lang.org/docu/files/ScalaReference.pdf

您还可以确认此检查编译器源代码： https://github.com/scala/scala/blob/946b76ad8b31b1fd74e2f8e1972c4a9159ac690a/src/reflect/scala/reflect/internal/StdNames.scala

// Compiler utilized names
...
val delayedInit: NameType          = "delayedInit"
val delayedInitArg: NameType       = "delayedInit$body"

还有： https://github.com/scala/scala/blob/96df73d994097e3318d003ddef00194b711289a3/src/reflect/scala/reflect/internal/Definitions.scala

// classes with special meanings
lazy val StringAddClass             = requiredClass[scala.runtime.StringAdd]
lazy val ScalaNumberClass           = requiredClass[scala.math.ScalaNumber]
lazy val TraitSetterAnnotationClass = requiredClass[scala.runtime.TraitSetter]
lazy val DelayedInitClass           = requiredClass[scala.DelayedInit]
  def delayedInitMethod = getMemberMethod(DelayedInitClass, nme.delayedInit)

scala App类DelayedInit钩子

1 个答案: