[Email-SIG] API for email threading library?

[Bill Janssen]

Thanks for all the feedback, folks.

After musing about all of this, it seems to me that threading makes no
sense outside the context of a message store (or forum post store, or
netnews article store, or...).  So I'm going to push all the decisions
about "what's a message anyway" into an abstraction of such a message
store:

   class ThreadableObjectStore:

      @abstractmethod
      get_message_id(msg) => message-ID (string)

      @abstractmethod
      get_subject(msg) => subject (string)

      @abstractmethod
      get_date(msg) => timestamp (float, seconds past epoch)

      @abstractmethod
      get_references(msg) => sequence of message-ID (list of string)

So your particular instantiation of ThreadableObjectStore can decide
what a 'msg' is, what a message-ID is, whether they're normalized, etc.
An instance of a ThreadableObjectStore will be required to create an
instance of a threadset.  I'll provide such a class for mailbox.Mailbox,
for testing.

Also, I think that persistence of the threading analysis is really a
function of the message store, not the threadset.  So what the threadset
requires is simply

  (1) a way to externalize its threads in a meaningful way, which a
      forest of tuple trees with message IDs at the nodes works perfectly
      well for, and

  (2) a way to take such a representation and revivify it, given a
      message store.

Bill