scala - 保理应用特征

Question

我有一个使用 App 的应用程序trait，而且一切正常。但是object继承自 App变得有点笨拙，所以我想将一些功能拆分为特征。特别是，我想拆分命令行参数处理。

不幸的是，这似乎不适用于 DelayedInit .所以这很好用:

object Main extends App {
  println("arguments are: "+ args.mkString.mkString(", "))
}

但这会抛出 NullPointerException :

trait CommandLineArguments { this: App =>
  println("arguments are: "+ args.mkString.mkString(", "))
}

object Main extends App with CommandLineArguments

有什么办法可以拿到 DelayedInit “包括”混合特征？

Answer 1

看起来很奇怪，如果像这样写一些，效果很好:

trait CommandLineArguments { self: App => 
  delayedInit {
     println("arguments are: "+ args.mkString.mkString(", "))
  }
}

但是来自 scaladocs (http://www.scala-lang.org/api/current/index.html#scala.DelayedInit):

Classes and traits inheriting the DelayedInit marker trait will have their initialization code rewritten as follows.[Code] becomes delayedInit([Code]) Initialization code comprises all statements and all value definitions that are executed during initialization.