How to do “Deep Copy” in Swift?

Question

In Objective-C, one can deep-copy by following:

 Foo *foo = [[Foo alloc] init];
 Foo *foo2 = foo.copy;

How to do this deep-copy in Swift?

Answer 1

To My Forgetful Future Self:

For anyone else looking for an easy way to do deep copy of a tree-style object with Swift (parent may/may not have children and those children may/may not have children & so on)…

If you have your classes set up for NSCoding (for persistent data between launches), I was able to use that ability to do a deep copy of any particular instance of this tree structure by doing the following…

(Swift 4)

class Foo: NSObject, NSCoding {
   var title = ""
   var children: [Foo] = []

   *blah, blah, blah*

   // MARK: NSCoding
   override public func encode(with coder: NSCoder) {
      super.encode(with: coder)
      coder.encode(title as Any?, forKey: "title")
      coder.encode(children as Any?, forKey: "children")
   }

   required public init?(coder decoder: NSCoder) {
      super.init(coder: decoder)
      self.title = decoder.decodeObject(forKey: "title") as? String ?? ""
      self.children = decoder.decodeObject(forKey: "children") as? [Foo] ?? []
   }

}

Meanwhile… Elsewhere…

// rootFoo is some instance of a class Foo that has an array of child Foos that each can have their own same array

// Archive the given instance
let archive = NSKeyedArchiver.archivedData(withRootObject: rootFoo)

// Unarchive into a new instance
if let newFoo = NSKeyedUnarchiver.unarchiveObject(with: archive) as? Foo {

   // newFoo has identical copies of all the children, not references

}