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scalaforeachunchecked

Scala: where to put the @unchecked annotation in a foreach

I have the following:

samples.sliding(2).foreach{case List(a, b)=> printf("%x %x\n", a.value, b.value)}

I know that the single 'case' will match all the possible values but I get a 'match is not exhaustive' warning. The Scala book explains where to put the @unchecked annotation on a normal fully-specified match expression, but not for the form above. How do I annotate the above to stop the compiler from complaining?

Solution

  • @unchecked is only defined for the selector in a match operation, not for arbitrary functions. So you could

    foreach{ x => (x: @unchecked) => x match { case List(a,b) => ... } }

    but that is rather a mouthful.

    Alternatively, you could create a method that unsafely converts a partial function to a complete one (which actually just casts to the function superclass of PartialFunction):

    def checkless[A,B](pf: PartialFunction[A,B]): A => B = pf: A => B

    and then you can

    samples.sliding(2).foreach(checkless{
  case List(a,b) => printf("%x %x\n", a.value, b.value)
})

    and you don't have any warnings because it was expecting a partial function.