[PATCH] Filter: picking community elements and finding min/max element

[Ondrej Zajicek]

On Thu, Dec 16, 2021 at 02:41:28PM +0100, Alexander Zubkov wrote:
> Hi everyone!
> 
> I made a couple of patches to do some interesting stuff with communities.
> The first patch allows to pick a component from a standard or a large community:
> 
> (10, 20, 30) @ 2 --> 20
> 
> And the second patch allows to search for minimum or maximum element
> in a community list. This combined allows to do some cool stuff with
> communities like this:
> 
> bgp_local_pref = filter(bgp_large_community, [(<as>, <localpref_val>,
> *)]).min @ 3
> 
> This will find us the minimum from our "localpref" communities and get
> that number as integer, ready to assign it where we need. Now we use a
> series of if's to check all the possible variants and that is not very
> convenient. I think this features will greatly boost the possibilities
> of working with communities in bird.

Hi

Nice patches, thanks! I agree that these features are pretty useful.
Will merge the second one with no comments.

With the first one, i do not really like the syntax. (Large) communities
are not arrays to access them with indexing operator, and also using '@'
as indexing operator is pretty unortodox. These are regular structures,
so it is natural to use structure field accessors. Question is how these
fields should be named, perhaps: global_id, data_1, data_2?

That would make:

(10, 20, 30) . global_id --> 10
(10, 20, 30) . data_1 --> 20

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."