Travis Griggs Travis Griggs - 5 months ago 12
Swift Question

NSData from hex String?

I know this question has been asked for

ObjectiveC
, but my
Swift
isn't strong enough yet to transliterate the
char *bytes
stuff.

So given

let string = "600DBEEF"


How do I create an
NSData
which represents those 4 bytes:
60 0D BE EF
?

Answer

With the arrival of Swift3 and the new Foundation Data type, I finally circled back to this:

extension UnicodeScalar {
    var hexNibble:UInt8 {
        let value = self.value
        if 48 <= value && value <= 57 {
            return UInt8(value - 48)
        }
        else if 65 <= value && value <= 70 {
            return UInt8(value - 55)
        }
        else if 97 <= value && value <= 102 {
            return UInt8(value - 87)
        }
        fatalError("\(self) not a legal hex nibble")
    }
}

extension Data {
    init(hex:String) {
        let scalars = hex.unicodeScalars
        var bytes = Array<UInt8>(repeating: 0, count: (scalars.count + 1) >> 1)
        for (index, scalar) in scalars.enumerated() {
            var nibble = scalar.hexNibble
            if index & 1 == 0 {
                nibble <<= 4
            }
            bytes[index >> 1] |= nibble
        }
        self = Data(bytes: bytes)
    }
}

Now I can construct Data objects in a fashion similar to their printed form:

Data(hex: "600dBeef")