Re: [Arx-users] Further thoughts on ArX and simplicity

[Kevin Smith]

Walter Landry wrote:
> Kevin Smith <address@hidden> wrote:
>
> > > > An archive is be a collection of branches. Each branch is an ordered 
> > > > collection of patches.
> > >
> > >
> > > Right now, everything is ordered.  But with revision hashes, they
> > > would become partially ordered.  That is inevitable if you are going
> > > to allow two people to work independently on the same line of
> > > development.
> >
> > Can you define "partially ordered" for me?
>
>
> If you have three revisions A, B, and C, you might be able to say that B
> and C come after A, but you can't say whether B comes before or after C.

Ah. Would it be accurate to say that *conceptually* a branch would be 
partially ordered, but a branch *as stored in a particular archive* 
would be fully ordered? If not, how would you represent partial ordering 
on disk?

With the current ArX format, there is effectively a "vector" of patches, 
due to the ,nn directory naming. If you switch to hashes, would you 
still represent a vector by listing the hashes in a text file somewhere, 
or would you switch to more of a linked-list where each revision would 
point to its parent(s)? Or both?

> > I must have been thinking of revisions, since (I guess) patches wouldn't 
> > have sequence numbers.
>
> Now you are confusing me.  Both patches and revisions have sequence
> numbers.  In mathematical terms, patches are the dual of revisions.

Oh. I was thinking that a "patch" was essentially a diff/patch file, 
whereas a "revision" was a patch within the context of a branch, thus 
having a revision number. But it looks like a revision can contain 
multiple patches.

I'm not a math/science guy, so "dual" doesn't really help.

I wish we had a wiki so we could have an easily maintainable glossary.

> > Hm. So given a patch that's already in a revision in my branch, and a 
> > patch that someone sends me, how would ArX know whether or not that 
> > patch was already in my branch? I thought that was how cherry-picking 
> > got into this discussion, but I guess not.
>
>
> ArX looks at the embedded name of the patch.  If you did something
> like change the metadata, then you have a different patch.  Metadata
> is important too.

What is the "embedded name"? Is that just the commit text? Or is it the 
hash of the patch+metadata?

> It is unlikely that you will get exactly the same patch from two
> sources.  Some people will agglomerate different fixes, change
> whitespace in different ways, etc.  The most likely way is that
> someone will submit an ordinary, non-ArX patch that two different
> people will incorporate.
>
> Moreover, it _is_ important to know that Fred has approved a patch
> rather than Wilma, since we know who is the real boss ;)

Ok. I guess I'm convinced. I haven't worked much with the patch utility, 
but I suppose it can tell if the same patch (with different metadata) 
has already been applied, so we don't need to pre-detect that case 
specially. Regardles, I'll take your word for it.

Kevin