Bug 25287

(In reply to comment #0)
> Is there any reason that Client objects must be immutable?

Service-activatable Clients with a .client file have to be immutable in order to avoid the .client file being full of lies.

Non-activatable Clients are immutable to avoid adding more complexity to an already-subtle spec; it took quite a long time to get ChannelDispatcher designed and implemented in MC 5, and we still haven't quite finished getting MC 5 to implement the spec *correctly* :-)

> Rob says, it would be nice to have a backwards compatible way of notifying the
> CD of changes to a client's filters.

That way is to have multiple Client heads. Empathy implements two clients, Empathy (service-activatable for basic functionality - Text at the moment, I think?), and Empathy.MoreThanMeetsTheEye (bonus functionality like file transfers and VoIP).

Adding a filter: add a Client head (then optionally remove any old Client head that is a subset of the new one)

Removing a filter: add a Client head with the appropriate subset of filters, then remove the old Client head that had the superset

Based on implementation experience, we could consider having change-notification in Telepathy 1.0, but my instinct is to say that that would add more complexity than it was worth. The ChannelDispatcher has to deal with Clients appearing and disappearing *anyway*, so if we make the filters immutable and use multi-headed Clients to implement filter changes, we get that functionality without any extra code.

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