filters: strange protocol restarts

[Sergey Popovich]

В письме от 27 сентября 2013 17:07:55 пользователь Ondrej Zajicek написал:
> It is documented:
> 
> Special operators include <cf/˜/ for "is element of a set"
> operation - it can be used on element and set of elements of the same
> type (returning true if element is contained in the given set), ...
> or on clist and pair/quad set (returning true if there is an element of
> the clist that is also a member of the pair/quad set)
> 

Yes, really. But is not clear to me how to use this to test for
community/ext community is non-empty.

> Well, that was my first idea w.r.t. the original problem with reconfigure,
> but having nonsensical '<' offends my algebraic sense ;-) and there is no
> good reason to imlement some consistent arbitrary ordering on such objects.
> 
> Good solution would be to have val_same(), which would work on all types
> (and would be used where equality is tested), while val_compare would only
> work on ordered objects.
> 
> You are right that pm_path_compare() already returns some nonsense.
> 

Thats my first idea. See [PATCH 03/12] in series.

> Well, these constants are not documented on purpose, as they are more
> like ad-hoc constants for testing purposes, not much needed when you
> have X.empty operator.

Sure, no problem with ad-hoc constants, let them be *internal*. I just fix
comparison/assignment with these constants in [PATCH 03/12].

> X.empty operator could be documented, i wanted to do it already,
> the only problem i have with it is its name. When i see 'X.empty',
> i would think that 'empty' mainly as adjective (predicate
> for emptiness-testing), not as verb (operator of emptying).
> 
> Having some predicate that would return true/false whether the
> path/list/set is empty would be useful, but both cannot be named
> 'empty'. Perhaps name the former 'reset'? Or keep current 'empty' and
> use some other name for the predicate? Any comments on this?

No problem with name 'reset', but I think we should leave 'empty' for
extended attributes for compatibility and document only 'reset'.
This was done in [PATCH 06/12]. To determine if clist or eclist
is empty, I suggest to use 'len' operator as this currently implemented
for bgppath type, which is done in [PATCH 05/12].

I start new patch series based on this thread with changes to filtering
code. I hope BIRD developers and community found useful these patches.

-- 
SP5474-RIPE
Sergey Popovich