Konstantin Khomoutov wrote:
>>>> From what I read, detached heads are subject to garbage collection.
>>>
>>> No, HEAD is protected against garbage collecting. To be sure you
>>> should name a branch when switching branches, though reflog would
>>> protect you for 30 days (by default) even if you don't do that.
>>
>> So Git doesn't really support anonymous branching as part of a normal
>> workflow.
>
> I perceive a certain logical fallacy here: you cannot switch between
> anything anonymous because to switch, you should somehow identify
> something to switch to--a name in whatever sense we put into this word.
In Mercurial, you can just update to a particular changeset (and you
identify that changeset by repository-local revision number or globally
unique ID) and then commit again. The point is that there's no need to
give a label to a head in Mercurial (although you can if you want to, using
Mercurial bookmarks, which are basically the same as what Git uses).
Here's an example of anonymous branching:
c:\test>hg init
c:\test>echo test>foo
c:\test>hg commit --addremove -m initial
adding foo
c:\test>echo first>>foo
c:\test>hg commit -m first
c:\test>hg log
changeset: 1:3e895ec28d6c
tag: tip
user: tactical
date: Mon Sep 26 01:39:46 2011 +0100
summary: first
changeset: 0:b51644bb3450
user: tactical
date: Mon Sep 26 01:39:40 2011 +0100
summary: initial
c:\test>hg update 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
c:\test>echo second>>foo
c:\test>hg commit -m second
created new head
c:\test>hg glog
@ changeset: 2:35c82a7e7de1
| tag: tip
| parent: 0:b51644bb3450
| user: tactical
| date: Mon Sep 26 01:40:10 2011 +0100
| summary: second
|
| o changeset: 1:3e895ec28d6c
|/ user: tactical
| date: Mon Sep 26 01:39:46 2011 +0100
| summary: first
|
o changeset: 0:b51644bb3450
user: tactical
date: Mon Sep 26 01:39:40 2011 +0100
summary: initial
I now have two anonymous branches, and these will never be garbage
collected. I can easily update to either branch with "hg update 1" or "hg
update 2" (or "hg update 0" again, if i want to create yet another
anonymous branch).
> As I understand, by switching between branches in Mercurial you mean
> switching between directories with clones;
No. Clones are a different topic.
> As to branches, they do have names in Git but they are very loosely
> coupled with their names: tag a tip of some branch (to still have a
> handle on that tip commit) then delete that branch--there will be no
> traces of that branch's name left, the branch's name is not encoded in
> its history in any way.
Git branch names are basically the same as Mercurial bookmarks. The
difference is that in Mercurial you don't *have* to use bookmarks.
> The branch names is just a way to not mess with
> SHA-1 names of commits (and to have references to those commits to keep
> them out of consideration for garbage collection).
> Hence the idea to demand support for anonymous branches in Git's model
> is just unfounded.
I think it's simply a weakness of Git. There are zero problems with
anonymous branching in Mercurial, and it's a very powerful and simple
system.
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