extension String {
    private func convertFullWidthToHalfWidth(reverse: Bool) -> String {
        let str = NSMutableString(string: self) as CFMutableString
        CFStringTransform(str, nil, kCFStringTransformFullwidthHalfwidth, reverse)
        return str as String
    }

    var hankaku: String {
        return convertFullWidthToHalfWidth(false)
    }

    var zenkaku: String {
        return convertFullWidthToHalfWidth(true)
    }

    private func convertFullWidthToHalfWidthOnlyNumber(fullWidth: Bool) -> String {
        var str = self
        let pattern = fullWidth ? "[0-9]+" : "[０-９]+"
        let regex = try! NSRegularExpression(pattern: pattern, options: [])
        let results = regex.matchesInString(str, options: [], range: NSMakeRange(0, str.characters.count))

        results.reverse().forEach {
            let subStr = (str as NSString).substringWithRange($0.range)
            str = str.stringByReplacingOccurrencesOfString(
                subStr,
                withString: (fullWidth ? subStr.zenkaku : subStr.hankaku))
        }
        return str
    }
    var hankakuOnlyNumber: String {
        return convertFullWidthToHalfWidthOnlyNumber(false)
    }

    var zenkakuOnlyNumber: String {
        return convertFullWidthToHalfWidthOnlyNumber(true)
    }
}