Swift Regex matching fails when source contains un

I'm trying to do a simple regex match using NSRegularExpression, but I'm having some problems matching the string when the source contains multibyte characters:

let string = "D 9"

// The following matches (any characters)(SPACE)(numbers)(any characters)
let pattern = "([\\s\\S]*) ([0-9]*)(.*)"

let slen : Int = string.lengthOfBytesUsingEncoding(NSUTF8StringEncoding)

var error: NSError? = nil

var regex = NSRegularExpression(pattern: pattern, options: NSRegularExpressionOptions.DotMatchesLineSeparators, error: &error)

var result = regex?.stringByReplacingMatchesInString(string, options: nil, range: NSRange(location:0,
length:slen), withTemplate: "First \"$1\" Second: \"$2\"")

The code above returns "D" and "9" as expected

If I now change the first line to include a UK 'Pound' currency symbol as follows:

let string = "£ 9"

Then the match doesn't work, even though the ([\\s\\S]*) part of the expression should still match any leading characters.

I understand that the £ symbol will take two bytes but the wildcard leading match should ignore those shouldn't it?

Can anyone explain what is going on here please?

It can be confusing. The first parameter of stringByReplacingMatchesInString() is mapped from NSString in Objective-C to String in Swift, but the range: parameter is still an NSRange. Therefore you have to specify the range in the units used by NSString (which is the number of UTF-16 code points):

var result = regex?.stringByReplacingMatchesInString(string,
        options: nil,
        range: NSRange(location:0, length:(string as NSString).length),
        withTemplate: "First \"$1\" Second: \"$2\"")

Alternatively you can use count(string.utf16) instead of (string as NSString).length .

Full example:

let string = "£ 9"

let pattern = "([\\s\\S]*) ([0-9]*)(.*)"
var error: NSError? = nil
let regex = NSRegularExpression(pattern: pattern,
        options: NSRegularExpressionOptions.DotMatchesLineSeparators,
        error: &error)!

let result = regex.stringByReplacingMatchesInString(string,
    options: nil,
    range: NSRange(location:0, length:(string as NSString).length),
    withTemplate: "First \"$1\" Second: \"$2\"")
println(result)
// First "£" Second: "9"