How do I use negative numbers in a range in Swift?

Question

I have the following code:

switch self.score
        {
        case 1:
            self.score = self.score - 2
        case -10...-10000: // ! Expected expression after unary operator
            println("lowest score")
            self.score = -10
        default:
            self.score = self.score - 1
        }

I have also tried case -1000...-10:. Both get the same error ! Expected expression after unary operator.

What I would really like to do is case <= -10:, but I can't figure out how to that without getting this error Unary operator cannot be separated from its operand.

What am I not understanding?

Try wrapping in parentheses maybe? – Rufflewind Jan 03 '15 at 15:19 — Rufflewind, Jan 03 '15 at 15:19
Unfortunately that doesn't work either. – webmagnets Jan 03 '15 at 15:23 — webmagnets, Jan 03 '15 at 15:23

Martin R · Accepted Answer · 2019-06-14T06:51:20.830

19

In the context of a switch case, a ... b is a "closed interval" and the start must be less or equal to the end of the interval. Also a plus or minus sign must be separated from ... by a space (or the number enclosed in parentheses), so both

case -10000...(-10):
case -10000 ... -10:

work.

case <= -10: can be written in Swift using a "where clause":

case let x where x <= -10:

Starting with Swift 4 this can be written as a “one-sided range expression”:

case ...(-10):

edited Jun 14 '19 at 06:51

answered Jan 03 '15 at 15:26

Martin R

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@webmagnets: In the "Where" section of the documentation: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/ControlFlow.html: *"A switch case can use a where clause to check for additional conditions ..."* – Martin R Jan 03 '15 at 15:30

How do I use negative numbers in a range in Swift?

1 Answers1