Sunday, October 13, 2013

Next step

We build a simple project/branch/version hierarchical abstraction, and we implement it on top of the core layer.

  • a project is a collection of branches that represent alternative ways the state evolves. Every project has a main branch.
  • A branch is a collection of versions that represent the evolution of the branch state over time.
  • A version is a collection of change-sets with some trappings.
  • A change-set is our unit of change.
When we do a read/write transaction, we'll add a new change set to the repository. Read-only transactions will specify a version for reading the core objects. Or two versions for generating diffs. Or maybe even three versions for a three-way merge.

Under this development model, developers will sync their workspace with the most chronologically recent version of the main branch. Their new change sets will be visible only to them, unless (until, we hope) they are "promoted" into the development branch.

We wanted to encourage frequent incremental check-ins. We wanted hook this up to Emacs autosave. Frequent check-ins of much smaller diffs breaks even.

Once you get to the point where your code passes all the tests, you promote it into the branch so everyone can use it. Every now and then the admins will "fork a relase", do some "cherrypicks" and make a release branch in the project.

Once you get to the point where your code passes all the tests, you promote it into the branch so everyone can use it. Every now and then the admins will "fork a relase", do some "cherrypicks" and make a release branch in the project.

The core code does all the heavy lifting, this is window dressing. The style: minimalist. Skin the change model.

This is turning into the code equivalent of a power-point lecture. You can read it yourself, I'm not going to walk you through it.

So that's it? Is that all there is? Many source code or change management systems do something more or less similar to this with files and directory trees instead of CLOS objects. Cute hack, but why all the fuss? Hasn't this been done?

If it seems obvious to you how we'd implement some of the usual source code control operations, good. We don't have to train you.

I wont insult your intelligence explaining in detail how to do a rollback by removing a change-set from a version. Use SETF, of course.

I hope nobody notices the 300 lb chicken sitting next to that shady-looking egg in the corner.

And something for philosopher/implementors to worry about: If I demote the change-set that instantiates an object, where does the object go? Is it possible create a reference to an uninstantiated object? What happens if you try to follow it?


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