git rebase

May. 31st, 2013 04:09 pm
[personal profile] mulhern_at_yocto
Two years ago I used git for a bit because GitHub uses git and GitHub was convenient for my needs at that time.

This allowed me to make one observation of some societal interest. People who use GitHub may not even know that "GitHub" is a portmanteau word, i.e., git + hub. In fact, they may not know about the existence of git at all. To some GitHub is just the same as DropBox, only, in some indefinable and mysterious way, cooler, and only for text. I don't know how that happened and how many people actually use it that way, but that some do is a fact.

Now, I knew that, in certain very important ways, git was not just like Subversion. It was, I was told, one of the new kind of distributed VCSs. Of course, in a perfect world I would have rapidly learned to exploit everything that was different, and perhaps better, about git. But I was very busy and git could be used just like Subversion and so...that's what I did.

Back when I was involved in a research project w/ multiple developers using Subversion I noticed a kind of pattern. A colleague would commit a change that affected a whole bunch of files and changed a lot of lines. Then, they would commit a bunch of small changes, one after the other, that really should have gone in with the initial commit. Often the note attached to the commit was just something very basic like "Should have gone in with previous." of "fixes a small bug in previous commit." or something like that. I often thought how nice it would be if all those little emendations could somehow be attached or combined to the original commit that got it all started. But in Subversion, you can't really do any sort of combining of commits without having superpowers and doing lots of fancy stuff. That kind of thing is just not part of the expected Subversion workflow.

Well, in git you can split, combine, and otherwise edit your commits freely using the git rebase command. This is because git divides your actions into two phases, whereas Subversion just has a single phase. In git, when you commit, you have only completed the first phase and you've only affected the copy of the code that you have. You haven't yet "pushed" your changes to some remote repository (which probably exists so that it can be shared with someone else). So you can rearrange all the commits in your private copy in many ways before you expose your work to the rest of the world by pushing it.

On the other hand, Subversion's commit combines git's commit and git's push into a single action.

How, really, will this difference change how I develop code and inflict it on the outside world? Will it make things better or just more nerve-wracking? We shall see.



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