Swift 5.1 Regex Bug - swift

Question

for the following code:
import Foundation
extension String {
var fullRange: NSRange {
return .init(self.startIndex ..< self.endIndex, in: self)
}
public subscript(range: Range<Int>) -> Self.SubSequence {
let st = self.index(self.startIndex, offsetBy: range.startIndex)
let ed = self.index(self.startIndex, offsetBy: range.endIndex)
let sub = self[st ..< ed]
return sub
}
func split(regex pattern: String) throws -> [String] {
let regex = try NSRegularExpression.init(pattern: pattern, options: [])
let fRange = self.fullRange
let match = regex.matches(in: self, options: [], range: fRange)
var list = [String]()
var start = 0
for m in match {
let r = m.range
let end = r.location
list.append(String(self[start ..< end]))
start = end + r.length
}
if start < self.count {
list.append(String(self[start ..< self.count]))
}
return list
}
}
print(try! "مرتفع جداً\nVery High".split(regex: "\n"))
the output should be :
["مرتفع جداً", "Very High"]
but instead it is:
["مرتفع جداً\n", "ery High"]
that because regex (for this case) matched the \n at the offset 10 instead of 9
is there any thing wrong in my code, or it is a bug in swift with regex !!

Answer 1

It's not a bug. You are trying to use Int indexes which is error-prone and strongly discouraged in an Unicode environment.
This is the equivalent of your code with the proper String.Index type and the dedicated API to convert NSRange to Range<String.Index> and vice versa. fullRange and subscript are obsolete.
I just left out the print line. startIndex and endIndex are properties of String
extension String {
func split(regex pattern: String) throws -> [String] {
let regex = try NSRegularExpression(pattern: pattern)
let matches = regex.matches(in: self, range: NSRange(startIndex..., in: self))
var list = [String]()
var start = startIndex
for match in matches {
let range = Range(match.range, in: self)!
let end = range.lowerBound
list.append(String(self[start..<end]))
start = range.upperBound
}
if start < endIndex {
list.append(String(self[start..<endIndex]))
}
return list
}
}
print(try! "مرتفع جداً\nVery High".split(regex: "\n"))
The result is ["مرتفع جداً", "Very High"]

Answer 2

I found the issue behind this bug?!
Swift Strings are so much weirder than any other language; since every character is 4 bytes length, then a single character (may, would, will, ..) contains 1 or 2 unicode characters (witch what happened in my case), so the solution is to subarray the unicodeScalars of the swift String instead of the string it self !!