Persistent data structure and git

From Wikipedia:

a persistent data structure is a data structure that always preserves the previous version of itself when it is modified. Such data structures are effectively immutable, as their operations do not update the structure in-place, but instead always yield a new updated structure.

Git own objects database is a persistence data structure.

Consider git repo with the following log:

commit 5a19382be2d700129a0c0ca81340a8858075501b (HEAD -> master)
Author: Muhammad Hewedy <mhewedy@gmail.com>
Date:   Tue Mar 19 23:35:34 2019 +0300

    Modifing menu

commit 64dba215678c5a888c178990da7186f8ada939b0
Author: Muhammad Hewedy <mhewedy@gmail.com>
Date:   Tue Mar 19 23:11:35 2019 +0300

    First Commit

When catting the latest commit, and the one previous to it, they will share the same unchanged element.

lets check the latest commit:

$ git cat-file -p 5a19382be2d700129a0c0ca81340a8858075501b
tree 80c92c5fa5a179dec9d7f6f0b81b45dd7d32742d
parent 64dba215678c5a888c178990da7186f8ada939b0
author Muhammad Hewedy <mhewedy@gmail.com> 1553027734 +0300
committer Muhammad Hewedy <mhewedy@gmail.com> 1553027734 +0300

Modifing menu

$ git cat-file -p 80c92c5fa5a179dec9d7f6f0b81b45dd7d32742d
100644 blob 3e34d35b8b00e443866d4e9fcbb152a308497147 menu.txt
040000 tree 9cbe2293128382f7d60125add044260f8630012a recipes

Now let's check its parent commit (the first commit):

$ git cat-file -p 64dba215678c5a888c178990da7186f8ada939b0
tree 8ae44ec1b6ef7e4b66eb7be36fba1046081d7128
author Muhammad Hewedy <mhewedy@gmail.com> 1553026295 +0300
committer Muhammad Hewedy <mhewedy@gmail.com> 1553026295 +0300

First Commit

$ git cat-file -p 8ae44ec1b6ef7e4b66eb7be36fba1046081d7128
100644 blob 23991897e13e47ed0adb91a0082c31c82fe0cbe5 menu.txt
040000 tree 9cbe2293128382f7d60125add044260f8630012a recipes

The recipes tree has not been changed, and since both commits share it, however, the menu.txt file has been changed, so each commit links to its own version.

In the end, the head of the persistent data structure always refers to the latest version of it. with the ability to track every single change.