When you do a checkout or reset etc. you are indeed operating on snapshots. You're just saying "get me this version right here".
But when you do cherry-pick or rebase etc, git is operating on diffs. A cherry-pick doesn't set your head or workdir to that version[0], it applies the changes to a new commit that sits on top of your current head. Similarly, a rebase walks through the changes and applies each one to the target.
Commits and diffs are a duality and it matters not one bit how git stores them underneath. You can always calculate one from the other.
[0] If you did want to do that for some reason then git reset will do it for you. That sets your current branch to that commit and with --hard it makes your workdir match. `git checkout <sha1> .` makes your workdir match that older commit, but it doesn't do deletes. If you want to make just your workdir match an older commit the only way I know is something like: `git reset --hard <sha1>; git reset --soft HEAD@{1}` which can be read as "set my current branch to be at sha1 and make working directory match that snapshot exactly, then set my branch to be at where it was before that operation, leaving my workdir alone". It's not a very common thing to want to do.
When you do a checkout or reset etc. you are indeed operating on snapshots. You're just saying "get me this version right here".
But when you do cherry-pick or rebase etc, git is operating on diffs. A cherry-pick doesn't set your head or workdir to that version[0], it applies the changes to a new commit that sits on top of your current head. Similarly, a rebase walks through the changes and applies each one to the target.
Commits and diffs are a duality and it matters not one bit how git stores them underneath. You can always calculate one from the other.
[0] If you did want to do that for some reason then git reset will do it for you. That sets your current branch to that commit and with --hard it makes your workdir match. `git checkout <sha1> .` makes your workdir match that older commit, but it doesn't do deletes. If you want to make just your workdir match an older commit the only way I know is something like: `git reset --hard <sha1>; git reset --soft HEAD@{1}` which can be read as "set my current branch to be at sha1 and make working directory match that snapshot exactly, then set my branch to be at where it was before that operation, leaving my workdir alone". It's not a very common thing to want to do.