Re: [gentoo-user] Re: Portage is proposing an ncurses update and I don't understand what it means

[Alan McKinnon]

On 02/09/2015 15:04, Neil Bothwick wrote:
> On Wed, 2 Sep 2015 05:24:33 -0700, walt wrote:
>
>> If the devs can't explain slots to their
>> users then they don't understand it themselves.  (Hm.  That phrase
>> sounds familiar.  Where did I get that?)
>
> I think it is an Einstein quote that says something like "if you can't
> explain it in simple terms, you don't understand it". He was probably
> having a pop at Niels Bohr and quantum theory at the time.
>
> Bohr said something like "if thinking about quantum theory doesn't give
> you a headache, you don't understand it".
>
>

And Feynmann said something along the lines of "Anyone who claims to
understand quantum mechanics, doesn't".

Back to subslots and not replying to Neil directly: They aren't that
hard to grasp, they look like this:

cat/pkg/pkg-1.2:3/4

The SLOT is 3 and the subslot is 4. As usual, different versions of the
same package in different SLOTs can co-exist. Subslots are a different
matter, and it's an unfortunate choice of name, as they are *not* a
subset of a SLOT. Look at ncurses:

[I] sys-libs/ncurses
     Available versions:
     (0)    5.9-r3 (~)5.9-r4 5.9-r5(0/5) (~)6.0-r1(0/6)
     (5)    5.9-r99(5/5) (~)5.9-r101(5/5) (~)6.0(5/6)

There's 2 SLOTs (0 and 5), and both have versions of subslot 5 and 6.
Subslots are most useful for things like api/abi versions where upstream
breaks these but don't increment the major version, this is why we had
endless issues in the past where emerge world broke stuff horribly and
it only got fixed much later when we could run revdep-rebuild. Nowadays
we have better tools, if the subslot changes for a consumed library,
then all consuming packages need to be rebuilt.

Describing and defining subslots is not hard, neither are the operators.
The problem with subslots is the usual one - you have to deal with real
life, and in real life upstreams sometimes do peculiar things to their
code that doesn't exactly match the effect of a subslot operation.

Or put another way: subslot docs describe the effect you should end up
with, it's not always the same thing as what you *do* end up with.
Finding that out means testing every possible circumstances and seeing
the results, but there's an infinite variety of those.


-- 
Alan McKinnon
alan.mckinnon@×××××.com