Re: Intro and questions

On 25 Jul 2001 15:37:49 +0000, Justus Pendleton wrote:
> peter.westlake@arm.com writes:
>
> > one where the sub-module would be thought of as "part of" the parent
> > module, and branched with it
>
> Why don't subdirectories suffice for this?

Because there's a distinct version history for the subproject.

It's really most useful for avoiding the "frequent merge" problem
of project-oriented versioning. That is, every time anyone changes
anything, anywhere in a large project, you need to do a merge before
a checkin.

If you have a large number of programmers working on a system, that
gets to be extremely irritating - every time you do a merge, you need
to recheck the system to make sure nothing broke, and then someone
else did a checkin while you were testing, so you need to merge again...

With subprojects, you checkout a complete version of the system.
Then you work on your subproject. You do checkins and merges against
your small piece of the project, which are only visible to other people
working on the subproject. Then the subproject reaches a stable point,
and you check the subproject into the parent project.

The changes to the master parent project become less frequent, and
people worry less about interfering with one another; plus you get the
additional advantage that you can put in tentative changes for other
workers on the subproject to evaluate, without worrying about breaking
the build for everyone working on the system.

If you've got a good solid branch system, then you're pretty close to
being able to do subprojects. There's just a little bit of
infrastructure
that needs to be added, and it works. (Think of a subproject as a
branch where you're only allowed to checkin changes to a specified
subset of the system.)

        -Mark

--
Mark Craig Chu-Carroll,  IBM T.J. Watson Research Center 
<mcc@watson.ibm.com>
*** The Synedra project:
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