模式匹配匿名

Question

I'm trying to do something like:

private val isOne = (x: Int) => x == 1
private val isTwo = (x: int) => x == 2

def main(x: Int): String = {
  x match {
    case isOne => "it's one!"
    case isTwo => "it's two!"
    case _ => ":( It's not one or two"
  }
}

Unfortunately... doesn't look like my syntax is right or maybe that's just no possible in Scala... any suggestions?

Answer 1

This isn't going to work for two reasons. First,

case isOne => ...

is not what you think it is. isOne within the match is just a symbol that will eagerly match anything, and not a reference to the val isOne . You can fix this by using backticks.

case `isOne` => ...

But this still won't do what you think it does. x is an Int , and isOne is a Int => Boolean , which means they will never match. You can sort of fix it like this:

def main(x: Int): String = {
  x match {
    case x if(isOne(x)) => "it's one!"
    case x if(isTwo(x)) => "it's two!"
    case _ => ":( It's not one or two"
  }
}

But this isn't very useful, and case 1 => .... does the job just fine.