Re: How to reset selected lines?

> Git's index and trees only understand whole files, so at some point you
> must generate the final file content. A diff is an easy way to represent
> the changes, apply them to the existing state, and then get that final
> content. But it doesn't _have_ to be. You could make some modifications
> to what is in the working tree and then say "OK, now stage this.".
>
> BUT. That is probably not what the user wants, if the content in the
> index actually has some modifications that are not in the working tree
> (i.e., you wouldn't want to overwrite them). Hence we tend to work with
> diffs, saying "make these changes to what is already in the index, and
> if they conflict, then bail".
>
> So "git add -p", for example, also works by creating diffs, modifying
> them, and feeding the result to "apply". You can see the implementation
> in git-add--interactive.perl, where it literally calls diff and apply
> commands.
>
> And that leads us to the answer to the first question. That script
> implements "add -p", but also "checkout -p" (which is what you want),
> "reset -p", "stash -p", etc. They differ only in what we diff and how we
> apply the result; the main engine of slicing and dicing the diff through
> user interaction is the same. See the %patch_modes hash for the list.