Now that Swift's Array's are truly immutable thanks to full value semantics, how can I create an mutable copy of an immutable array? Similar to Obj-C mutableCopy(). I can of course downcast the array to an NSArray and use mutableCopy() but don't want to use NSArray because it does not strictly typed.
I have a toolbar which has items from the storyboard. I want to remove an item from the toolbar and use toolbar.setItems. I wanted to do it without casting as a NSArray, because none of these functions take NSArrays, they take [AnyObject].
Obviously now when I call removeAtIndex() it does not work, which is correct. I just need a mutableCopy
Simply assigning to var does not work for me and give 'Immutable value of type [AnyObject]'
var toolbarItems = self.toolbar.items
toolbarItems.removeAtIndex(2) //Immutable value of type [AnyObject]
I am using Beta 3
The problem is that self.toolbar.items is an implicitly unwrapped optional (of type [AnyObject]!) and they are always immutable. When you assign to the variable toolbarItems without explicitly stating its type, it too becomes an implicitly unwrapped optional, and thus is immutable as well.
To fix this do either:
var toolbarItems:[AnyObject] = self.toolbar.items
toolbarItems.removeAtIndex(2)
Or:
var toolbarItems = self.toolbar.items as [AnyObject]
toolbarItems.removeAtIndex(2)
Update
As of Xcode 6 Beta 5, you can update collections that are stored in optional variables, so the original code now works:
var toolbarItems = self.toolbar.items
toolbarItems.removeAtIndex(2)
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
