为什么出现此错误：类型不匹配； 找到：所需单位：字符串=>单位

Question

Below code :

object gen {
  println("Welcome to the Scala worksheet")

  case class CS(funToRun: String => Unit)

  val l: List[CS] = List(

    CS(open("filePath"))

    )

  def open(path: String): Unit = {
    java.awt.Desktop.getDesktop.open(new java.io.File(path))
  }
}

causes compiler error :

type mismatch; found : Unit required: String => Unit

But my open function is of of type String => Unit and param type of funToRun is String => Unit ?

Answer 1

CS accepts a function from String to Unit , but you're passing to it the result of open , which is Unit .

If you want to pass it open as a function instead, you need to do:

CS(open)

although without knowing what you're trying to achieve, it's impossibile to provide a sensible solution.

A possible alternative for performing the open action at a later time

case class CS(funToRun: () => Unit) // the function is not taking parameters any longer
val cs = CS(() => open("filePath")) // 'open' is not performed here
cs.funToRun() // 'open' is performed here

This way the open function is not evaluated when passed to the CS constructor.