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

[Fernando Rodriguez]

On Thursday, September 03, 2015 9:10:26 AM walt wrote:
> On Wed, 2 Sep 2015 15:34:43 +0200
> Alan McKinnon <alan.mckinnon@×××××.com> wrote:
>
> > 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.
>
> I just updated my virtualbox ~amd64 guest and all went well when I ran
> emerge ncurses:5/5, so I'm encouraged but not fearless about doing the
> same on my real machine.  I'm going to be quickpkged to the max before
> I try it.
>
> BTW, emerge world on the vbox guest did not offer to touch ncurses in
> any way.  I had to do it manually as I just said.
>
> Leveraging Neil's quote:  thinking about slots (and their misnamed
> subslots) gives me a 4-dimensional headache.

I don't think they're misnamed, the problem is in our heads. As end users 
we've come to accept that they can be co-installed as the defining property of 
slots. But they're about the same in every other way AFAIU.

-- 
Fernando Rodriguez