LinkedList: NSCoding protocol

In my previous post I’ve explained that the new Codable protocol of Swift 4 has some problems with references to objects (i.e. class instances). Or, better said, the two implementations of coders available

  • ProperListEncoder/PropertyListDecoder
  • JSONEncoder/JSONDecoder

have this problem: they expand all references to new objects and create doublets if references in the object tree occur more than once for a single object. In the case of loops in the object tree (references of objects to each other) the encoding leads to an endless loop.

The old NSKeyedArchiver/NSKeyedUnarchiver of the Objective C-world do not have this problem: they respect references and restore them correctly at unarchiving. So, I want to implement this old way, i.e. the NSCoding protocol in my LinkedList as well. Remark: LinkedList uses references to its payload as well even in loops but that is taking care of even in the use of the Coding protocol.

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LinkedList: Codable protocol and references

Maybe you have read my series of posts about LinkedLists. It was great fun for me to put these things together, but recently, I stumbled over a problem with serialisation, esp. the Codable protocol and references to objects. In Swift 5 there are two Encoder/Decoder pairs available:

  • PropertyListEncoder/PropertyListDecoder
  • JSONEncoder/JSONDecoder

It turns out that these encoders are not really suitable for archiving object graphs because they expand all references to objects, i.e. put the objects instead of the references in the archive. If you have a simple tree of objects and you do not care about doublets that may be fine but as soon as you have loops in your object graph you are in trouble. Encoding such a graph with these two encoders lead to an endless loop. This may happen quite frequently; just think about delegation where you typically have references of the delegate and its master against each other.

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Animate NSView’s scrollToVisible

When I ported my game Empire for macOS (see: https://apps.apple.com/de/app/empire/id1287139467?mt=12) to iOS (see: https://apps.apple.com/de/app/empire-mobile/id1465452819) I noticed a much nicer scrolling behaviour there. There are a lot of smaller and more fundamental differences in programming for these two operating systems, especially between AppKit and UIKit and animation is one of them.

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