Performance comparison of JSONDecoder and JSONSerializaton decoding and returning a struct from a 7 MB JSON.
macOS: JSONEncoder was 10.95% slower than JSONSerialization + object mapping.
Linux: JSONEncoder was 0.28% faster than JSONSerialization + object mapping.
The JSONEncoder bars show performance of decoder.decode() where decoder is a previously instantiated JSONDecoder.
The JSONSerialization bars show the total performance of JSONSerialization.jsonObject, a cast of that return value to [String: Any], and then instantiating a struct from that dictionary.
Borrowed ideas from JSONShootout. Also using their large JSON file.