Swift 3 conversion emcompassing muliple issues - swift3

Question

I have started converting to swift 3 while removing NS classes as much as possible, but ran into a snag with his code:
var S: String = ADataItem.description_text;
// FRegExBufui_Image is of type NSRegularExpression
let matches: [NSTextCheckingResult] = FRegexBufUI_Image.matches(in: S, options: NSRegularExpression.MatchingOptions(), range: NSRange(location: 0, length: S.characters.count));
if matches.count > 0 {
for m in 0 ..< matches.count {
S = S.substring(with: match.rangeAt(m));
I get error
Cannot convert value of type 'NSRange' (aka '_NSRange') to expected
argument type 'Range'
(aka'Range')
I think maybe the reason for the problem is I am now mixing swift datatypes/classes with NS.
The mos clean solution here... is that simply casting NSRange to Range? Or is there a way to go fully Swift when I need to use regular expressions as well?

Answer 1

A Swift Range and an NSRange are different things. It looks like the function is expecting a Swift range which you can create using the ..< operator. Instead of
NSRange(location: 0, length: S.characters.count)
write
0 ..< S.characters.count
Note that the above two things are not identical in semantics although they both represent the same set of characters. The NSRange takes the start location and the length of the character sequence. The Swift Range uses the lower and upper bound (the upper bound is excluded).

Answer 2

The easiest way is to bridge the string to NSString
let matches = FRegexBufUI_Image.matches(in: S, options: NSRegularExpression.MatchingOptions(), range: NSRange(location: 0, length: S.characters.count));
for match in matches { // don't use ugly C-style index based loops
let substring = (S as NSString).substring(with: match.rangeAt(m))
}
If you don't want to use mixed types implement this String extension which converts Range<String.Index> to NSRange:
extension String {
func range(from nsRange: NSRange) -> Range<String.Index>? {
guard
let from16 = utf16.index(utf16.startIndex, offsetBy: nsRange.location, limitedBy: utf16.endIndex),
let to16 = utf16.index(from16, offsetBy: nsRange.length, limitedBy: utf16.endIndex),
let from = String.Index(from16, within: self),
let to = String.Index(to16, within: self)
else { return nil }
return from ..< to
}
func substring(withNSRange range : NSRange) -> String
{
let swiftRange = self.range(from : range)
return swiftRange != nil ? self.substring(with: swiftRange!) : self
}
}
and use it:
for match in matches { // don't use ugly C-style index based loops
let substring = S.substring(withNSRange: match.rangeAt(m))
}
Edit:
In Swift 4+ the extension has become obsolete. There is a convenience initializer to create Range<String.Index> from NSRange
for match in matches { // don't use ugly C-style index based loops
let stringRange = Range(match.range(at: m), in: S)!
let substring = String(S[stringRange])
}