Scala：模式匹配多个Option参数

Question

I would like to achieve something like the following:

  private def msgPrefix(implicit myClass: MyClass, anotherClass: AnotherClass) = {        
    Option(myClass, anotherClass) match {
      case Some(validMyClass, validAnotherClass) => validMyClass.process + validAnotherClass.process
      case _       => ""
    }
  }

What is the right way to do this?

Answer 1

I'm not sure I understood what you're looking for, but :

 private def msgPrefix(implicit myClass: MyClass, anotherClass: AnotherClass) = {        
   (Option(myClass), Option(anotherClass)) match {
     case (Some(validMyClass), Some(validAnotherClass)) => validMyClass.process + validAnotherClass.process
     case _ => ""
   }
 }

This will return the empty String if at least one of the two arguments is null, ie :

scala> msgPrefix(MyClass("foo"),null)
res2: String = ""

scala> msgPrefix(MyClass("foo"),AnotherClass("bar"))
res3: String = foobar

But you probably should just change the type of the arguments to Option[MyClass] and Option[AnotherClass] (if you can).

Answer 2

I agree with Marth that your arguments should probably be Option[MyClass] and Option[AnotherClass] . But to answer your original question, you can use a for comprehension rather than pattern matching:

private def msgPrefix(implicit myClass: MyClass, anotherClass: AnotherClass) = {
  val prefix = for {
    validMyClass <- Option(myClass)
    validAnotherClass <- Option(anotherClass)
  } yield validMyClass.process + validAnotherClass.process
  prefix.getOrElse("")
}