Iterating through string backwards through iterator in Swift

Question

I have this code:

var formatterIndex = hourFormattingPattern.endIndex
let formattingPatternRange = formatterIndex ..< hourFormattingPattern.startIndex

But I'm getting an error of bad access when the second line is called. Is there a way to specify a range that reverses through the string hourFormattingPattern? After the initialization, I'm doing this:

while !stop {
    //Do pattern matching and switching with string and replace char string
    formatterIndex = formatterIndex.predecessor()

    if formatterIndex <= hourFormattingPattern.endIndex || tempIndex <= tempString.endIndex {
         stop = true
     }

 }

Any help appreciated. Thank you

What exactly are you trying to do? You can iterative backwards with for index in (hourFormattingPattern.startIndex ..< hourFormattingPattern.endIndex).reverse() { } — Code Different
– Code Different, Commented Jul 7, 2016 at 2:34

andyvn22 · Accepted Answer · 2016-07-07 02:59:34Z

2

Yes, you can't form a range from a larger number to a smaller one. Also, endIndex is not a valid index--it's one past the last valid index. You can, however, form your range forwards and then reverse it:

var formatterIndex = hourFormattingPattern.endIndex
let formattingPatternRange = hourFormattingPattern.startIndex..<formatterIndex

for formatterIndex in formattingPatternRange.reversed() where !stop {
    //Do pattern matching and switching with string and replace char string

    if formatterIndex <= hourFormattingPattern.endIndex || tempIndex <= tempString.endIndex {
        stop = true
    }
}

However, your logic may be off, because all possible values of formatterIndex are <= hourFormattingPattern.endIndex, and thus stop will be set true on the first run of your loop.

answered Jul 7, 2016 at 2:59

andyvn22

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