Re: Consistent terminology: cached/staged/index

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Feb 26, 2011, 20:36 UTC
Message-ID: <AANLkTincNdUQ=736=M2Oei4LF0pR0c2T7r=bWJE3RFCu@mail.gmail.com>
In-Reply-To: <1297897887.24521.57.camel@drew-northup.unet.maine.edu>

On Thu, Feb 17, 2011 at 1:11 AM, Drew Northup <drew.northup@maine.edu> wrote:

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>
> On Sun, 2011-02-13 at 19:09 -0800, Pete Harlan wrote:
>> On 02/13/2011 02:58 PM, Junio C Hamano wrote:
>> >> --staged
>> >> ~~~~~~~~
>> >> diff takes --staged, but that is only to support some people's habits.
>> > The term "stage" comes from "staging area", a term people used to explain
>> > the concept of the index by saying "The index holds set of contents to be
>> > made into the next commit; it is _like_ the staging area".
>> >
>> > My feeling is that "to stage" is primarily used, outside "git" circle, as
>> > a logistics term.  If you find it easier to visualize the concept of the
>> > index with "staging area" ("an area where troops and equipment in transit
>> > are assembled before a military operation", you may find it easier to say
>> > "stage this path ('git add path')", instead of "adding to the set of
>> > contents...".
>>
>> FWIW, when teaching Git I have found that users immediately understand
>> "staging area", while "index" and "cache" confuse them.
>>
>> "Index" means to them a numerical index into a data structure.
>> "Cache" is a local copy of something that exists remotely.  Neither
>> word describes the concept correctly from a user's perspective.
>
> According to the dictionary (actually, more than one) "cache" is a
> hidden storage space. I'm pretty sure that's the sense most global and
> therefore most appropriate to thinking about Git. (It certainly
> describes correctly what web browser cache and on-CPU cache is doing.)
> One would only think the definition you gave applied if they didn't know
> that squirrels "cache" nuts. I don't think that the problem is the
> idiom.

Not really. If a squirrel "caches" nuts, it means a squirrel is putting them in a hidden place to save them for future use. So, in the future, if said squirrel wants a nut, it doesn't have to look for it in the trees, just go to the cache. So the cache makes it easier to access whatever your want.

IOW; if you don't cache something, you would have more trouble getting it, but you still can.

That's not what Git is doing. Git is not putting changes in a place so the can be more easily accessed in the future. It is using a temporary device that allows the commit to be built through an extended period of time. It's not a cache.

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>> I learned long ago to type "index" and "cached", but when talking (and
>> thinking) about Git I find "the staging area" gets the point across
>> very clearly and moves Git from interesting techie-tool to
>> world-dominating SCM territory.  I'm surprised that that experience
>> isn't universal.
>
> Perhaps that helps you associate it with other SCM/VCS software, but it
> didn't help me. When I realized that the "index" is called that BECAUSE
> IT IS AN INDEX (of content/data states for a pending commit operation)
> the sky cleared and the sun came out.

That's not an index. An index is a guide of pointers to something else. It allows you to find whatever you are looking for by looking in small table of pointers instead of looking through all the samples.

IOW; if you don't index something, you would have more trouble finding it, but you still can.

That's not what Git is doing.

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> In all reality the closest thing Git has to an actual staging area is
> all of the objects in .git/objects only recorded by the index itself.
> Git-stored objects not compressed into pack files could technically be
> described as "cached" using the standard definition--they aren't visible
> in the working directory. Unfortunately this probably just muddies the
> water for all too many users.

That's irrelevant. You can implement the same functionality in many other ways. How it is implement doesn't matter, what matters is what the user experiences.

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> So, in summary--the index is real, objects "cached" pending
> commit/cleanup/packing are real; any "staging area" is a rhetorical
> combination of the two. Given that rhetorical device may not work in all
> languages (as Junio mentioned earlier) I don't recommend that we rely on
> it.

Branches and tags are "rthetorical" devices as well. But behind scenes they are just refs. Shall we disregard 'branch' and 'tag'?

No. What Git does behind scenes is irrelevant to the user. What matters is what the device does, not how it is implemented; the implementation might change. "Stage" is the perfect word; both verb and a noun that express a temporary space where things are prepared for their final form.

-- 
Felipe Contreras