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Swift cannot assign immutable value of type NSData

I have

let data = NSData(bytes: &positionValue, length: sizeof(UInt8))

and

let dataString=NSString(bytes: &data, length: sizeof(UInt8), encoding: NSUTF8StringEncoding)

Unfortunately, the compiler throws an error on the second line saying that it cannot assign an immutable value of type NSData. How do I go about converting the original variable data

to an encoded string SUTF8StringEncoding

?

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2 answers


update: Xcode 7.2 • Swift 2.1.1



let myTestString = "Hello World"

// converting from string to NSData
if let myStringData = myTestString.dataUsingEncoding(NSUTF8StringEncoding) {

    // converting from NSData to String
    let myStringFromData = String(data: myStringData, encoding: NSUTF8StringEncoding) ?? "Hello World"
}
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I don't quite understand what you are trying to achieve since it has not been explained what positionValue

(it is apparently some byte value).

Regardless, the error message comes from being used &

with a constant (generated let

). &

provides an unsafe pointer that allows you to manipulate the memory containing the constant value, but you cannot change the constant, which is why Swift throws an error message.

If you change the first line to read

var data = NSData(bytes: &positionValue, length: sizeof(UInt8))


then it is data

no longer a constant but a variable, and you can use &

with it.

Having said all this, since it data

contains the byte (s) you want to convert to a string, you can simply say

let data = NSData(bytes: &positionValue, length: sizeof(UInt8))
let dataString=NSString(data: data, encoding: NSUTF8StringEncoding)
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