How does one create a mutable copy of an immutable array in swift?

Arrays are value types (struct), so they are passed around by value and not by reference.

That said, if you create a variable of array type and assign it the immutable array, a copy of the immutable array is actually created and assigned to it - and of course that copy has no relationship with the original immutable array (besides having the same values at the time it is created).

let immutable = [1, 2, 3]

//immutable[0] = 1 // Fails, ok

var mutable = immutable

mutable[0] = 5

In your case, you are accessing an immutable array which is an NSArray of AnyObjects (see documentation). You can use it as an Array in swift, make a copy of it and modify as follows:

let immutable : NSArray = [ 1, 2, 3 ]

//immutable[0] = 1 // Fails, ok

var mutable : [AnyObject] = immutable

mutable.removeAtIndex(1) // mutable now is [1, 3]

mutable[0] = 7 // mutable now is [7, 3]

After you're done with your changes, you can assign to the items property

It is as simple as declaring a var with your array.

var items = toolbar.items

Now you can change items and then reassign to the toolbar.

toolbar.items = items

Note that you can cannot (as of Beta 3) alter the elements of an "immutable" array declared with let as well. Just the length of the array is was fixed, which is why you cannot remove items.

However, according to Apple's documentation of UIToolbar, the items array is already mutable.

SWIFT
var items: [AnyObject]!

Tested + works:

    var mutable : [UIBarButtonItem] = []
    for button in toolbar.items {
        mutable += button as UIBarButtonItem
    }
    mutable.removeAtIndex(2)
    toolbar.setItems(mutable, animated: true)

TO REMOVE AN OBJECT FROM PARTICULAR INDEX OF AN ARRAY.

let fullArray : NSArray = Userdefaults().value(forKey: "YOUR_ARRAY_STRING") as! NSArray
var mutableArray : [AnyObject] = fullArray as [AnyObject]
mutableArray.remove(at: INDEX_TO_REMOVE) //Eg: mutableArray.remove(at: 0)
mutableArray.append(ARRAY_TO_APPEND)

In Beta3 constant arrays are completely immutable while variable arrays are entirely mutable. So just change let array:to var array: and then verify your code