gistfile1.swift

class MyClass : NSObject {
    
    var anArray:Array<String>?
    
    func printDebug() -> String {
        
        if (anArray != nil) {
            return "Array has \(anArray!.count) element(s)"
        } else {
            return "No array"
        }
    }
}

let mc = MyClass()
mc.printDebug()

var items = Array<String>()
items.append("Item 1")
var otherItems = items

// copy happens here
mc.anArray = items
mc.printDebug() // "Array has 1 element(s)"

items.append("Item 2") // ["Item 1", "Item 2"]
// since mc's array is a copy it's out of sync
mc.printDebug() // "Array has 1 element(s)"