使 NSDecimalNumber 可编码 [英] Making NSDecimalNumber Codable

问题描述

是否可以扩展 NSDecimalNumber 以符合 Encodable &可解码协议?

Is it possible to extend NSDecimalNumber to conform Encodable & Decodable protocols?

推荐答案

无法扩展 NSDecimalNumber 以符合 Encodable &可解码 协议.Jordan Rose 在以下 swift 进化电子邮件线程 中对此进行了解释.

It is not possible to extend NSDecimalNumber to conform to Encodable & Decodable protocols. Jordan Rose explains it in the following swift evolution email thread.

如果您需要在 API 中输入 NSDecimalValue 类型，您可以围绕 Decimal 构建计算属性.

If you need NSDecimalValue type in your API you can build computed property around Decimal.

struct YourType: Codable {
    var decimalNumber: NSDecimalNumber {
        get { return NSDecimalNumber(decimal: decimalValue) }
        set { decimalValue = newValue.decimalValue }
    }
    private var decimalValue: Decimal
}

顺便说一句.如果您使用 NSNumberFormatter 进行解析，请注意 已知错误 在某些情况下会导致精度损失.

Btw. If you are using NSNumberFormatter for parsing, beware of a known bug that causes precision loss in some cases.

let f = NumberFormatter()
f.generatesDecimalNumbers = true
f.locale = Locale(identifier: "en_US_POSIX")
let z = f.number(from: "8.3")!
// z.decimalValue._exponent is not -1
// z.decimalValue._mantissa is not (83, 0, 0, 0, 0, 0, 0, 0)

以这种方式解析字符串:

Parse strings this way instead:

NSDecimalNumber(string: "8.3", locale: Locale(identifier: "en_US_POSIX"))

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