Swift 4's new Codable protocol makes it much simpler to serialize Swift objects. The built-in JSONEncoder and PlistEncoder encode and decode JSON and plist, but what about when you need to use other formats?
Writing a custom encoder is fairly complex, so Serializer takes care of that for you. Serializer converts your Swift objects into a simple enum, which you can easily traverse and write to a file format of your choice.
All you have to do is implement the Serializer protocol and create a method called serialize, which encodes a Serializable enum into your custom format. Decoding is similar -- add the Deserializer protocol, with a deserialize method which converts your custom format into a Serializable. Here's an example serializer and deserializer for the NBT file format.