Lesson 2: Version Control System

Claude

2024-10-16

Version Control System

git is a Distributed Version Control System

Version Control System
Revision Control System
Source Control System
Source Code Management

https://git-scm.com/

What is a DVCS

A VCS keeps older versions of your files
Like an “undo” button on steroids
- Keep all history forever
- History contains all files, any file types
- Each change has a “note / comment”
- See older versions and see changes between versions, without actually “undoing”
- Undo one specific change
- Trees of changes
And then all of this distributed, multi-user.

Caveat: you have to manually create the undo-steps.

In practice

Let’s make it visual
Once you have tasted the power, you never want to go back

start

add man

add cat

add faces on man and cat

add piano on string

Make piano on string obey the laws of physics

Replace piano by safe

Colour cat

Give man a hat

Give cat an aura

v10

Get a second winch for string

v11

“Timeline”

timeline

The steps in order, with short names and version numbers

Revision-line

revisionline

It might make as much sense, to name the changes (not the images)

Environment

When I was working here, I wanted to experiment with adding some environment

Add a sun

v7*

Add houses and a tree

v8*

Note that I decide what goes together into a revision

Add a river

v9*

Add a car

v10*

New revisionline

revisionline-with-environ

Speech bubbles

Also at some point I looked into speech bubbles

Wisecracks

v6**

Note that this frame makes sense, however this would not make sense together with the sun.

More realistic response

v7**

New revisionline

revisionline-with-2-branches

Even more complex

revisionline-with-branches

Tree

root

Tree with branches

branchpoints

Two similar trees

revisionline-with-branches

Alternative

revisionline-with-branches-alt

Trees and branches in git

In git you work with repositories
A repository is a tree with (usually) a single root
The tree consists of commits (aka revisions)
It has one or more branches, all running from the root to the tip
Each branch has a name
A branch does not have to “stick out”, you can even have two branches completely overlap
Default branch name is main or master

Branches

drawn-branches

Why do we need a repository

Undo specific commit

“Undo” normally allows undoing of the last action.
- In VCS, you can revert any commit
- e.g. once the drawing is finished, you could do git revert v4, what would happen?

The faces should be removed from the final image

Note that sometimes a later commit depends on a previous one, meaning manual fixing is needed.

Separation of features

By doing certain things in separate branches, you can try things without polluting the stable code.
e.g. I could experiment adding text bubbles, and only decide later if I needed them
It means that if you have a function, you could work on some changes, but still keep the original function until your changes are done

Merge two branches

It’s possible merge two branches.
If we are on the main branch, and type git merge environment, what should happen?

The changes in the environment branch should be “imported”, so there will be all the changes in the main branch, and the sun/house/tree/car.

Also here, this may not always be possible automatic, or the result may not always make sense. e.g. import the speech-bubbles branch into the environment branch.

Cherry-pick certain commits

It’s not necessary to merge whole branches, but e.g. only import the commit that adds the car to the main branch.

Different people can work on different branches

And then sync through something like GitHub

History, attribution and comments

At any time it’s possible to see the full history of the repository, and go to any spot in the tree
At this spot, new branches can be started
The history will show who did a certain commit and show the commit message.
Git tools also allow you to see in the current code, when a certain line was last changed and by whom.