Re: What is the mechanism of a git checkout?

From: Jakub Narebski <jnareb@gmail.com>
Date: May 29, 2009, 09:05 UTC
Message-ID: <m3hbz4b7ov.fsf@localhost.localdomain>
In-Reply-To: <slrnh1udov.6ls.sitaramc@sitaramc.homelinux.net>

Sitaram Chamarty <sitaramc@gmail.com> writes:

Show 16 quoted lines

> On 2009-05-28 15:21:59, mastermindxs <mastermindxs@gmail.com> wrote:
> >
> > does a git checkout pull the contents of a branch? how does it
> > physically separate files in your working directory from other
> > branches?
> >
> > The speed of which it works leads me to the logical conclusion
> > that the files in the working directory are all there for all
> > branches and git simply only shows you the files of the active
> > branch.
> >
> > Can anyone shed more light on the underlying mechanisms of git
> > checkout maybe even branch and merge as well?
> 
> I explain it as below when I get asked this question.  It's
> a simplified answer but largely correct, I believe.

[...]

Show 12 quoted lines

>   - files that do show up in "git status" in the "before"
>     branch, are either modified or staged.
>     
>     - if the "before" branch version is the same as the
>       "after" branch version, that also is not touched.  In
>       the new branch, running "git status" will show you the
>       same files.
> 
>     - if the "before" branch version and the "after" branch
>       version are *not* the same, git would lose your local
>       (uncommitted) changes, so it refuses to do the
>       checkout and stays where it is.

In which case (there is file which is different in "before" and "after", and which is modified in working area) you can ask git to try to 'move' (merge) changes from "before" to "after" version of a file with '-m' / --merge option, see git-checkout(1):

  git checkout -m after

-- 
Jakub Narebski
Poland
ShadeHawk on #git