CODEWITHSUNDEEP
swiftnsdata
Stephan
Stephan

Reputation: 4263

Struct into NSData

This is quite clear and works:

struct DEMO {
   var used: Bool = false;
}

var a = DEMO()
var dataA = NSData(bytesNoCopy: &a, length: sizeof(DEMO))

This make sense because this method uses a CMutableVoidPointer.

Now use a const:

let b = DEMO(used:true)
var dataC = NSData(bytes: &b, length: sizeof(DEMO)) // ERROR
var dataB = NSData(bytesNoCopy: &b, length: sizeof(DEMO))  // ERROR

And you get an error on both init methodes, but why?

Do I really have to copy first a const into a var to use it?

var c = b
var dataC = NSData(bytes: &c, length: sizeof(DEMO))

I think this is why it is a similar problem within a function, you get a "let":

func test(data: DEMO) {
  var c = NSData(bytes: data, length: sizeof(DEMO)) // ERROR
  var b = NSData(bytes: &data, length: sizeof(DEMO)) // ERROR
  var d = NSData(bytesNoCopy: data, length: sizeof(DEMO)) // ERROR
  var a = NSData(bytesNoCopy: &data, length: sizeof(DEMO)) // ERROR
}

All of them deliver errors.

How to handle swift const with NSData?

Upvotes: 1

Views: 2416

Answers (1)

Stephan
Stephan

Reputation: 4263

Based on Martin R comment I suggest a "work around" solution for the function part

func test(inout data: DEMO) {
  var a = NSData(bytesNoCopy: &data, length: sizeof(DEMO),freeWhenDone:false)

  .... 
}

The inout parameter provide at least a not cost version of data.

Upvotes: 1

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