It's just a different approach - sometimes understanding top-down is easier than bottom-up. The git code is pretty clean and simple, but pedagogically speaking

It's just a different approach - sometimes understanding top-down is easier than bottom-up. The git code is pretty clean and simple, but pedagogically speaking it's not super easy to get an understanding of everything without reading most of it. It's like reading a math paper where they define all the variables they use first before even getting to the main ideas. It's more rigorous, but not necessarily the most straightforward way to convey something. Also, you don't necessarily always care that something is a struct or a union or that it's implemented as a custom variant of a B+tree that does xyz or that there's this quirk on Solaris that causes filenames to be written on disk backwards or something.