Why is this code generating a scala match exception

Asked Apr 17 '19 at 15:29

Active Apr 17 '19 at 16:49

Viewed 49 times

I'm trying to compare two parallel arrays of strings together. Each array is guaranteed to be the same length. Corresponding strings in each array may be indented differently, so I perform a trim when comparing them. I've written the following function to do the comparison, and I'm getting a match error when I run the code:

def compare(expected: Seq[String], actual: Seq[String]): Boolean = (expected, actual) match {
    case (Nil, _) => true
    case (a :: _, b :: _) if (a.trim != b.trim) => false
    case (_ :: a, _ :: b) => compare(a, b)
}

What am I missing here? As far as I can tell this should cover all cases.

The actual exception:

 scala.MatchError: (WrappedArray(ExpectedString), WrappedArray(ActualString)) (of class scala.Tuple2)

edited Apr 17 '19 at 15:44

asked Apr 17 '19 at 15:29

Andy

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If you are going to pattern match against Lists, you should receive lists instead of generic sequence as parameters. Maybe, when calling the method you are not passing a List but maybe an Array or Vector? – Luis Miguel Mejía Suárez Apr 17 '19 at 15:31
Please share your exception. – Krzysztof Atłasik Apr 17 '19 at 15:31
@MichaelZajac Both sequences are guaranteed to be the same length. – Andy Apr 17 '19 at 15:42
@KrzysztofAtłasik added. – Andy Apr 17 '19 at 15:44
@Andy The error es pretty clear, you are passing a WrappedArray, but the method only works for Lists. – Luis Miguel Mejía Suárez Apr 17 '19 at 15:45
@LuisMiguelMejíaSuárez Why is that? – Andy Apr 17 '19 at 15:45
@Andy if you change the method signature to `def compare(expected: List[String], actual: List[String]): Boolean`. Then, it wont compile where you are using it, which is better than a runtime exception. – Luis Miguel Mejía Suárez Apr 17 '19 at 15:46

Why is this code generating a scala match exception

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