7 ms·

While the above is tecnobabble, there /is/ a simple way to state what git is. It's an API to interact with a torsor. We have files, which are inert objects and

• zitterbewegung 6y ago
  What do you think of darcs?
• matthiasv 6y ago
  While this sounds all nice it actually fails to model Git as it is. Git is an object database and its objects are blobs, trees and commits not diffs, so your premise is based on a misconception.
  • thaumasiotes 6y ago
    > Git is an object database and its objects are blobs, trees and commits not diffs What do you think is the difference between a "commit" and a "diff"?
    • detaro 6y ago
      A "commit" doesn't contain a diff, it contains (references to) the blobs of the files at that state. Diffs are display-only, generated by comparing two full file states.
      • thaumasiotes 6y ago
        You really believe that git stores -- in full -- every version of a tracked file? Every commit that deletes the whitespace from an otherwise empty line in a 30KB file is another 30KB of hard drive space gone?
        • detaro 6y ago
          The git book explains the internals very well, so you can easily verify it for yourself. Files are referenced as objects in trees, which are pointed to by commits. editing a file creates a new object for it. (edited for tone)
          • thaumasiotes 6y ago
            From the book: > You have two nearly identical 22K objects on your disk (each compressed to approximately 7K). Wouldn’t it be nice if Git could store one of them in full but then the second object only as the delta between it and the first? > It turns out that it can. The initial format in which Git saves objects on disk is called a “loose” object format. However, occasionally Git packs up several of these objects into a single binary file called a “packfile” in order to save space and be more efficient. Git does this if you have too many loose objects around, if you run the git gc command manually, or if you push to a remote server. > When Git packs objects, it looks for files that are named and sized similarly, and stores just the deltas from one version of the file to the next. You can look into the packfile and see what Git did to save space. https://git-scm.com/book/en/v2/Git-Internals-Packfiles https://git-scm.com/book/en/v2/Git-Internals-Packfiles
            • detaro 6y ago
              Which is explicitly a lower-level optimization applied to files well-suited for it and not related to the concept of a commit. A commit does not reference a diff.
              • thaumasiotes 6y ago
    • seppel 6y ago
      A diff is something that describes the changes between two versions but does NOT refer to any specific version; or at least it is something that can be worked with independent of any specific version. Ie. I can develop a fix for a issue for version 1.2.30 of some software, generate a the diff using the diff tool and then apply this diff using the patch tool to version 1.1.15 of the software. This might fail (or result in something undesired), but there no principal problem in moving the diff around and applying it somewhere else. A git commit however is a particular version, so git is not really good at applying a commit somewhere else.
  • kadoban 6y ago
    Git itself requires you be able to think of it as both models, diffs and snapshots. For example most uses of `git rebase` are clearer if your mental model while doing so are of diffs. That only one is how it's implemented is besides the point really, until you get _quite_ low level.
    • matthiasv 6y ago
      Of course when working with Git it makes sense to think in changesets. But OP was specifically modelling the technical side starting with "We have files, which are inert objects …".
  • kps 6y ago
    And that's a bigger problem with git than the horrible commands. Every project I've worked on that has used git has had a diff-based workflow, and sometimes the mismatch is painful — I wish I didn't have to know about `--full-history` and that `git show X` isn't necessarily the same as `git diff X^..X`. I really hope something like pijul takes off.
• psahgal 6y ago
  While this is a wonderful explanation for a person already familiar with mathematical concepts such as groupoids, torsors, and directed acyclic graphs, I think that this explanation is really unfriendly for the layman/novice developer who's just trying to get their changes up on Github.
• recursive 6y ago
  How is this any less technobabble? I looked up torsor on wikipedia. I learned nothing, except that "torsor" is a real word, and not just something you made up for a joke.
  • YeGoblynQueenne 6y ago
    How could you possibly not have learned anything by reading the wikipedia page for "torsor" that starts with the following? In algebraic geometry, given a smooth algebraic group G, a G-torsor or a principal G-bundle P over a scheme X is a scheme (or even algebraic space) with an action of G that is locally trivial in the given Grothendieck topology in the sense that the base change Y × X P {\displaystyle Y\times _{X}P} Y\times _{X}P along "some" covering map Y → X {\displaystyle Y\to X} Y\to X is the trivial torsor Y × G → Y {\displaystyle Y\times G\to Y} Y\times G\to Y (G acts only on the second factor).[1] Equivalently, a G-torsor P on X is a principal homogeneous space for the group scheme G X = X × G {\displaystyle G_{X}=X\times G} G_{X}=X\times G (i.e., G X {\displaystyle G_{X}} G_{X} acts simply transitively on P {\displaystyle P} P.) Look, there's even links to the sub-terms: ("algebraic group" article): In algebraic geometry, an algebraic group (or group variety) is a group that is an algebraic variety, such that the multiplication and inversion operations are given by regular maps on the variety. ("action" article): In algebraic geometry, an action of a group scheme is a generalization of a group action to a group scheme. Precisely, given a group S-scheme G, a left action of G on an S-scheme X is an S-morphism ("principal homogeneous space" article): In mathematics, a principal homogeneous space,[1] or torsor, for a group G is a homogeneous space X for G in which the stabilizer subgroup of every point is trivial. Equivalently, a principal homogeneous space for a group G is a non-empty set X on which G acts freely and transitively (meaning that, for any x, y in X, there exists a unique g in G such that x·g = y, where · denotes the (right) action of G on X). An analogous definition holds in other categories, where, for example, Really, all you have to do is read the article carefully and follow the links to unknown terminology if you can't immediately intuit its meaning. However, it's only just basic category theory, really. (yes, guys, /s).
    • sicariusnoctis 6y ago
      Dude probably doesn't even know what a co-Yoneda embedding is, either. smh
• kristopolous 6y ago
  What does simple mean to you?
• IAmNotAFix 6y ago
  All is well until you need merges, which is where the confusion happens and minds are lost. - You have a branch `master`. - You have a branch `feature` which contains commit C, which conflicts with `master`. - You merge `feature` into `master`, fixing conflicts. - You log the commits of `master`. * First is the merge commit, whose diff contains code added by commit C (including the conflict resolution). * Next you see commit C, whose diff contains code added by commit C (obviously) Wait, how can 2 commits in a row have a diff that modifies the code in the same way? Well, mind you, the diff of a commit doesn't correspond to the moment the patch of the commit was added to the current branch, it only corresponds to the moment it was added to its own branch.
  • yencabulator 6y ago
    The problem with that is thinking a directed acyclic graph is a flat sequential list. Try `git log --graph --oneline` or `gitk`.
• booleandilemma 6y ago
  It's an API to interact with a torsor Well why didn't you just say so!
• greggturkington 6y ago
  Ah, so just a file space with a rooted DAG where each node is a diff with paths manipulable by queries where diffs can use a groupoid action to produce a new file or conflict, resulting in an API to interact with a torsor.
• voldacar 6y ago
  this is your brain on category theory