Won Formatter

실시간 입력 받으면서 formatter를 적용시킬때 악몽이 떠올라서 제일 마지막으로 미뤄 뒀던 Formatter.
Int -> Formatted String
ex) 1000 -> 1,000
이렇게 바꿀꺼다.

참고
https://stackoverflow.com/questions/44630702/formatting-numbers-in-swift-3

extension String { var toLocale: Locale { return Locale(identifier: self) } }

extension NumberFormatter {
    convenience init(numberStyle: NumberFormatter.Style, groupingSeparator: String?, decimalSeparator: String?) {
        self.init()
        set(numberStyle: numberStyle, groupingSeparator: groupingSeparator, decimalSeparator: decimalSeparator)
    }

    convenience init(numberStyle: NumberFormatter.Style, locale: Locale) {
        self.init()
        set(numberStyle: numberStyle, locale: locale)
    }

    func set(numberStyle: NumberFormatter.Style, groupingSeparator: String?, decimalSeparator: String?) {
        self.locale = nil
        self.numberStyle = numberStyle
        self.groupingSeparator = groupingSeparator
        self.decimalSeparator = decimalSeparator
    }

    func set(numberStyle: NumberFormatter.Style, locale: Locale?) {
        self.numberStyle = numberStyle
        self.locale = locale
    }
}

extension Numeric {
    func format(formatter: NumberFormatter) -> String? {
        if let num = self as? NSNumber { return formatter.string(from: num) }
        return nil
    }
}