Roman Nums in Swift

Roman Nums.swift

//: Playground - noun: a place where people can play

import UIKit

extension Int {
    func toRoman() -> String? {
        var number = self
        
        guard number > 0 else {
            return nil
        }
        
        let values = [("M", 1000), ("CM", 900), ("D", 500), ("CD", 400), ("C",100), ("XC", 90), ("L",50), ("XL",40), ("X",10), ("IX", 9), ("V",5),("IV",4), ("I",1)]
        
        var result = ""
        
        for (romanChar, arabicValue) in values {
            let count = number / arabicValue
            
            if count == 0 { continue }
            
            for _ in 1...count
            {
                result += romanChar
                number -= arabicValue
            }
        }
        
        return result
    }
}

13.toRoman()
(12+15).toRoman()
2015.toRoman()
0.toRoman()

extension String {
    func toArabic() -> Int? {
        var string = self as String
        
        let values = [("M", 1000), ("CM", 900), ("D", 500), ("CD", 400), ("C",100), ("XC", 90), ("L",50), ("XL",40), ("X",10), ("IX", 9), ("V",5),("IV",4), ("I",1)]
        
        var result = 0
        
        for (romanChars, arabicValue) in values {
            let range = romanChars.startIndex ..< romanChars.endIndex
            
            while string.hasPrefix(romanChars) {
                result = result + arabicValue
                
                #if swift(>=3.0)
                string.removeSubrange(range)
                #else
                string.removeRange(range)
                #endif
            }
        }
        
        if (string.isEmpty) {
            return result
        }
        
        return nil
    }
}

"MCMXXV".toArabic()
"XIII".toArabic()
"R0B".toArabic()

Pretty much the same as the previous Swift versions, but this time I preferred to use removeRange rather than substringFromIndex

@kumo like this?

for (romanChars, arabicValue) in values {
    while string.hasPrefix(romanChars) {
        result = result + arabicValue        
        string = string.substringFromIndex(romanChars.endIndex)
    }
}

Using ..< for the range

Adding support for Swift 3 (removeSubrange instead of removeRange)