Git is a purely functional data structure (2013)
blog.jayway.com
Git is a purely functional data structure (2013)
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Re: Git is a purely functional data structure (2013)
#2I found the explanation from the Immutable JS presentation easier to understand when talking about Immutable data structures [0]
Re: Git is a purely functional data structure (2013)
#3Git is not a purely functional data structure [1]
[1] man git-rebase
Re: Git is a purely functional data structure (2013)
#4I often recommend people to read "Git Internals".
If you know how git works internally, it's much easier to understand how it works and the reasons behind it.
Re: Git is a purely functional data structure (2013)
#5Git is not a purely functional data structure [1] [1] man git-rebase
But git-rebase does not alter existing commits in the commit tree, it simply creates a new branch (meaning new commits) on the tree.
Re: Git is a purely functional data structure (2013)
#6Perhaps for those familiar with "functional data structures" such an analogy is helpful but I find it easier to simply explain git for what it is without adding more exotic nomenclature to it.
Git lets you do version control via full snapshots as opposed to just tracking diffs (even though it does actually do this too behind the scene).
You can think of a full snapshot as saving a copy of your project structure every time you do a commit. The key trick is that git doesn't actually create new copies of the content for each commit but simply maintains a tree structure whose nodes are pointers (via hashing) to the content they represent.
The complication from git is not in understanding the core concept but knowing how best to apply them. There are all sorts of crazy workflows you could implement by manipulating git pointers and their associated patches. As with anything that is flexible, difficulty comes in knowing how to constraint yourself when using it.
Re: Git is a purely functional data structure (2013)
#7Git is not a purely functional data structure [1] [1] man git-rebase
I don't see that anywhere. A rebase is just a fork.
Re: Git is a purely functional data structure (2013)
#8I often recommend people to read "Git Internals". If you know how git works internally, it's much easier to understand how it works and the reasons behind it. https://git-scm.com/book/en/v1/Git-Internals
Even more enlightening is The git Parable.
http://tom.preston-werner.com/2009/05/19/the-git-parable.htm...
Re: Git is a purely functional data structure (2013)
#9A data structure cannot be functional. I understand what he's trying to say, and agree with most of it, but the word "functional" is purely wrong. What he wants to say is "good". But not all "functional programming" is good, nor is all good programming functional by necessity, despite what your local Lambda The Ultimate nerd tries to tell you.
The Best, when it comes to data structures is a Directed, Acyclic Graph. For instance your typical linux filesystem is a DAG. But there's one problem with DAGs: When they reach a certain complexity human brains are not fit enough to parse them anymore. (programs still can though)
So in many circumstances at least a human programmer needs to take a look at the state of your program and make assumptions about its correctness, which is called debugging. And that's why in Good programs we often use Good data structures instead of The Best.
Good data structures are key->value stores (which you may know as "hash tables" or "dictionaries"), trees, and trees in a simplified special form: lists, each of them being somewhat able to represent the other two, if one can accept a performance hit and/or increased complexity in source code. Dictionaries, trees, lists. That's it. And you do that in every programming language that is at least a little bit interested in being Good.
So there's nothing special or functional about git's data structures, it's just normal Good programming, and a few programmers who are so good at programming that they don't even need to mention it anymore, they breath good programms.
Then of course to the normal bread-earning coder good programs are a rare sight. But the reason is not that they are really rare, the reason is that successful business doesn't really require Good programs to succeed. Mediocre programs are good enough to earn their rent, and most of us spend most of our coding hours to earn our rent.
All that being said, if you don't just want to make money, go and spend some time studying git internals. It will teach you a lot more than most of your teachers/professors taught you combined. Sadly the source code is written by Linux gurus, who like to encrypt their source code with a very special key that only people from their tribe can understand. But the Git Book is actually good enough that you can study quite a lot of the internals from that book. I also suggest writing your own git in your favorite programming language once, to really understand it.
Re: Git is a purely functional data structure (2013)
#10Git is not a purely functional data structure [1] [1] man git-rebase
If Git were purely functional, you would expect rebase not to modify the existing data in any way, and indeed that is exactly what happens. You can create, delete, or modify only the top-level pointers: branch names, reflog, etc. Instead, rebase creates a completely new set of commits, and points the current branch at a new one. This is exactly how functional data structures work in e.g. Haskell, where "inserting" an element into a dictionary means that you get a new copy of the dictionary, and all existing references to the original are unmodified.