Make a shallow copy of collection classes (Array, Dictionary) in swift, not a deep copy.

Question

There seems to be a lot of confusion and different opinions on this out there, I want to know, is that possible in swift to make a shallow copy of an object and not a deep copy.

I checked in JAVA - http://www.jusfortechies.com/java/core-java/deepcopy_and_shallowcopy.php, It's clearly explained the difference between shallow copy and deep copy with example, but I didn't got kind of example in swift.

I tried initWithArray:copyItems: to check what difference does it make when I'm changing the Boolean flag of copyItems, but none of the difference I see. I supposed to have difference of shallow or deep copy by changing the copyItems flag, but I was wrong it creates a deep copy always.

Please check my below code, I cloned the array object arrayObject1 to arrayObject2 using initWithArray:copyItems: by setting copyItems: to true. I changed the arrayObject2 0th string object to new string object and arrayObject2 0th object changed, but arrayObject1 0th object didn't changed. whereas if I'm copying it by assigning copyItems: to false, then also I'm having the same result.

So how to achieve a shallow copy and if it's not by initWithArray:copyItems: then what copyItems: flag making impact on result.

func createAnArrayUsingArrayCopyItems(){

        let name = "albort"
        let arrayObject1 = NSArray.init(objects: name, 15)
        let arrayObject2 = NSMutableArray.init(array: arrayObject1 as [AnyObject], copyItems: true)
        arrayObject2[0] = "john"
        print(arrayObject1)
        print(arrayObject2)

    }  

Output ->

Answer 1

It happens because name is a Swift String instance. String is struct, thus it's a value type. That is because it's always copied by value. arrayObject1 as [AnyObject] is a conversion to swift Array (a struct too) with String objects within.

So it's not trivial to get a shallow copy using such structures like Array and String in Swift.

I can only come up with an idea of boxing struct instances into a class wrapper:

class StringBox : CustomStringConvertible, NSCopying {
  var string: String

  init(str: String) {
    string = str
  }

  var description: String {
    return "\(string)"
  }

  @objc func copyWithZone(zone: NSZone) -> AnyObject {
    return StringBox(str: string)
  }
}

func createAnArrayUsingArrayCopyItems(){
  let name = StringBox(str: "albort")
  let arrayObject1 = NSArray.init(objects: name, 15)
  let arrayObject2 = NSMutableArray.init(array: arrayObject1 as [AnyObject], copyItems: false)
  (arrayObject2[0] as! StringBox).string = "john"
  print(arrayObject1[0])
  print(arrayObject2[0])
}

createAnArrayUsingArrayCopyItems()

It gives me a following output:

john
john