How to write a proper null-safe coalescing operator in scala?

醉酒当歌 提交于 2019-11-26 12:59:32

问题


Having seen the answers coming out of questions like this one involving horror shows like trying to catch the NPE and dredge the mangled name out of the stack trace, I am asking this question so I can answer it.

Comments or further improvements welcome.


回答1:


Like so:

case class ?:[T](x: T) {
  def apply(): T = x
  def apply[U >: Null](f: T => U): ?:[U] =
    if (x == null) ?:[U](null)
    else ?:[U](f(x))
}

And in action:

scala> val x = ?:("hel")(_ + "lo ")(_ * 2)(_ + "world")()
x: java.lang.String = hello hello world

scala> val x = ?:("hel")(_ + "lo ")(_ => (null: String))(_ + "world")()
x: java.lang.String = null


来源:https://stackoverflow.com/questions/1364361/how-to-write-a-proper-null-safe-coalescing-operator-in-scala

标签
易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!