Persistence and wire formats in Swift
May contain multiple explorations in this area.
I started this to explore some aspects of Codable as of Swift 4 in particular supporting polymorphic class hierarchies.
See the CodableHierarchies\README.md for a detailed explanation of how polymorphic behaviour with protocols can be easily encoded using Codable.
See the PersistedHierarchies\README.md for a detailed explanation of how this alternative works, using binary encoding and preserving a class hierarchy.
Note that it uses a more robust method of registering factories using a string key, as a contrast to the very dangerous approach in CodableHierarchies where we save an index and rely on the programmer to get their factory array right with unique indexes for each type!
There are multiple playgrounds in there exploring increasing features through to backward references.