Swift 是否可以限制 ExpressibleByIntegerLiteral struct 的初始值

我想实现数字 struct ，它应该由整型文字初始化.

喜欢:

let digit: Digit = 5

但SWIFT不应该允许这样做(或者，作为一种 Select ，应该提出例外):

let digit: Digit = 15

我写了这段代码，但看起来不太好:

   struct Digit: ExpressibleByIntegerLiteral, Equatable, CustomStringConvertible {
    
    typealias IntegerLiteralType = Int
    
    var description: String {
        String(value)
    }
    
    var value: IntegerLiteralType {
        // Unfortunately, set throws can't be implemented, only get throws.
        willSet(newValue) {
            if 0...9 ~= value {
                self.value = newValue
            }
        }
    }


    init(integerLiteral: IntegerLiteralType) {
        if 0...9 ~= integerLiteral {
            value = integerLiteral
        } else {
            // This is definitely not good and may cause side effects.
            // But init for ExpressibleByIntegerLiteral can't be failable.
            value = 0
        }
    }
    
    init?(from char: Character?) {
        guard let char,
              let newValue = IntegerLiteralType(String(char)),
              0...9 ~= newValue
        else {
            return nil
        }
        value = newValue
    }
}

在SWIFT 5.8中，我如何克服这一点？我猜在下一个版本中可能会使用宏，但不幸的是，我的SWIFT版本仍然没有它们.

谢谢.