[xentac]

I guess the big difference is the level of interaction. A Mercurial extension has access to all the functionality that Mercurial offers: applying patches, creating commits, history walking, etc. But it doesn't really modify the underlying representation of that data (queues store their data in the working copy, for example).

Git doesn't give you access to its functionality but instead gives access to its data model. Stashes are just references, commits are created or destroyed at will, notes are just objects that point at commits and are stored in a different set of references, etc.

[aredridel]

Interesting. I've never considered that git doesn't give access -- it's always seemed right there to me, whether I want to tweak it by calling out to a git tool to do it, or doing it myself.

[xentac]

It does, but instead of giving you a library/API access, like Mercurial, it gives you command line access. I feel as though one is a little more black box than the other.

[chrisrhoden]

Please see libgit/libgit2