how to use pattern match get a nonEmpty list in scala?

Question

I'm use case x :: Nil => ... attempt to make sure the list is nonEmpty, but it just match single element list.How can I use pattern match get a nonEmpty list?

UPDATED
I'm sorry,it seems I lose something, there is a special scene use the match inner,

object AccountResult{
  def unapply(account: AccountResult): Option[(String, List[String])] = ???
}

//ignore accountResult define please 
accountResult match {
  case AccountResult(_, x :: _) => ... 
}

how can I match accountResult which List[String] (x :: _) value is not Nil? and then get the matched List[String] value

Answer 1

Instead of specifying only the empty list with Nil, specify something that can be any list, eg.:

case x :: tail => ... // tail is a local variable just like x, holding the tail of the list

or simply:

case x :: _ => ...

if you don't care about or won't be using the tail.

These patterns will match any list with at least one element (rather than exactly one element as per your existing pattern). Similarly, the pattern:

case x :: y :: the_rest => ...

will match any list with at least two elements.

Edit (response to your comment):

You can assign to a variable within a case pattern, using "@". So, for (a typical usage) example that you may have seen already:

case acc@AccountResult(_, x :: tail) => ... // do something with 'acc'

or, matching the usage you are seeking per your comment:

case AccountResult(_, phone@(x :: tail)) => ... // do something with 'phone'

Answer 2

To check if list is non empty you can pattern match this way:

list match {
   case Nil => false
   case _ => true
}

Or

list match {
  case Nil => false
  case x::xs => true  
}

Answer 3

If you just want to assign a whole non-empty list to a val, without splitting head and tail, you just add a case matching an empty list, and another one assigning the list to a variable name like this:

accountResult match {
  case List() => ??? // empty case
  case myAccountResult => ??? //myAccountResult will contain the whole non-empty list  
}

Nil does the job as well, matching an empty list

accountResult match {
  case Nil => ??? // empty case
  case myAccountResult => ??? //myAccountResult will contain the whole non-empty list  
}