var session1 = Session(startTime: Date(), endTime: Date())
session1.events.append(Event(timeStamp: Date(), tag: "test session1/event1"))
session1.events.append(Event(timeStamp: Date(), tag: "test session1/event2"))
var session2 = Session(startTime: Date(), endTime: Date())
session2.events.append(Event(timeStamp: Date(), tag: "test session2/event1"))
session2.events.append(Event(timeStamp: Date(), tag: "test session2/event2"))
session2.events.append(Event(timeStamp: Date(), tag: "test session2/event3"))
let sessions: [Session] = [session1, session2]

let data = NSKeyedArchiver.archivedData(withRootObject: sessions.encoded)
let back = (NSKeyedUnarchiver.unarchiveObject(with: data) as? [Session.Coding])?.decoded
print(back ?? "error in getting back sessions")

/*
[
  Session(
    startTime: 2016-10-15 13:34:45 +0000, 
    endTime: Optional(2016-10-15 13:34:45 +0000), 
    events: [
      Event(timeStamp: 2016-10-15 13:34:45 +0000, eventTag: "test session1/event1"), 
      Event(timeStamp: 2016-10-15 13:34:45 +0000, eventTag: "test session1/event2")]), 
  Session(
    startTime: 2016-10-15 13:34:45 +0000, 
    endTime: Optional(2016-10-15 13:34:45 +0000), 
    events: [
      Event(timeStamp: 2016-10-15 13:34:45 +0000, eventTag: "test session2/event1"), 
      Event(timeStamp: 2016-10-15 13:34:45 +0000, eventTag: "test session2/event2"), 
      Event(timeStamp: 2016-10-15 13:34:45 +0000, eventTag: "test session2/event3")])]
*/