Re: Yet another multiple inheritence problem

Hi Jan,

I was hoping to better understand what's going on with your patch before 
responding, but that hasn't happened yet, so I figured I'd just respond.

I don't know anything about c3, but providing additional method 
invocation orders sounds nifty to me.

An alternative possible solution if you don't get c3 "complete" as you 
like it is that we could make eieio-default-superclass special in that 
it always shows up last on any invocation order.  In that way, you could 
sort your own classes to avoid problems without worrying about the 
default superclass.

Eric

Jan Moringen wrote:
> Hi,
> 
> I'm back with yet another multiple inheritance problem (too many mixins,
> I guess) ;)
> 
> My class graph looks like this:
> 
>                         eieio-default-superclass
>                                    |
>                +-------------------+-------------------+
>                |                   |                   |
>           rudel-state    rudel-impersonator    rudel-delegator
>                |                   |                   |
>                +-------------------+-------------------+
>                                    |
>                             rudel-obby-state     e-def-sup
>                                    |                |
>                   +----------------+                |
>                   |                                 |
>    rudel-obby-client-connection-state    rudel-obby-document-handler
>                   |                                 |
>                   +----------------+----------------+
>                                    |
>                   rudel-obby-client-state-subscribing
> 
> [In case the diagram gets messed up:
> 
> (defclass rudel-state ()
> (defclass rudel-impersonator () 
> (defclass rudel-delegator ()
> (defclass rudel-obby-state (rudel-state rudel-impersonator
> rudel-delegator)
> (defclass rudel-obby-client-connection-state (rudel-obby-state)
> (defclass rudel-obby-document-handler ()
> (defclass rudel-obby-client-state-subscribing
> (rudel-obby-client-connection-state rudel-obby-document-handler)
> 
> ]
> 
> The problem appears with an invocation of the generic function
> `no-applicable-method'. There is a method installed for
> `rudel-delegator' and, of course, for `eieio-default-superclass'. I
> expected the method for `rudel-delegator' to be called, since it is on
> the most specific class. On second thought, the breadth-first method
> resolution order cannot really do that, so the behavior is as expected.
> However, I would like a different behavior better.
> 
> Despite my current problem, I think the breadth-first search may not be
> optimal. A little searching yielded [1] in which the so-called C3
> algorithm is described. The points made there seem very logical to me.
> So much in fact, that I ported the implementation to Elisp and engaged
> in some experiments. As expected, my problem could be solved, were :c3
> available as a :method-invocation-order.
> 
> In my opinion, it would be very useful to include a :c3 method
> resolution order in EIEIO, or even make it the default.
> 
> I attached some code to reproduce the original problem, my c3
> implementation experiments and a patch that allows :c3 as
> a :method-invocation-order (it is not a complete implementation,
> though).
> 
> What do you think?
> 
> Kind regards,
> Jan
> 
> [1] http://192.220.96.201/dylan/linearization-oopsla96.html
> 
> 
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