Re: [boost] [git] Mercurial?

Subject: Re: [boost] [git] Mercurial?
From: Martin Geisler (mg_at_[hidden])
Date: 2012-03-21 04:41:59

Julian Gonggrijp <j.gonggrijp_at_[hidden]> writes:

Hi,

This discussion was mentioned on the Mercurial mailinglist. I'm a
Mercurial developer, but let me start by saying that you will be very
happy with both tools. DVCS is a great step up from SVN and people
rarely look back.

>> FWIW, I am the last person who will oppose such a change. But
>> currently, noone presented a fair reasoning in favor for git,
>
> Well, allow me to present some fair reasoning to you.
>
> With regard to git versus svn: I think enough fair reasons have been
> given why git (or a DVCS in general) is better than svn. I'm not going
> to repeat those arguments here.
>
> With regard to git versus mercurial: given that it's probably a good
> idea to switch to a DVCS, git and mercurial seem to be the primary
> candidates. I think everyone in this thread should be more willing to
> admit that they're close competitors. In many ways they're about
> equally "good", and when they aren't the differences are quite moot:
>
> - mercurial has native support for Windows, but git is also fairly
>   well supported on Windows and seems to be rapidly improving;

Yes, both tools work on Windows.

> - git allows you to edit history while mercurial doesn't, but which
>   you like better is a matter of preference;

This statement is *false*. I'm not sure where you've read it?

Both tools let you modify the history and with the same consequences.
Editing history really means creating a new history and throwing away
the old history and they both support this.

There is a non-technical difference, though: Mercurial has a *bias*
towards immutable history in its command set. Technically it can throw
away your history just like Git can throw it away.

> - git seems to be more "powerful" and less susceptible to errors,
>   while mercurial is said to have better documentation -- while this
>   doesn't make either objectively better than the other in the first
>   place, they're also both catching up on their weaker side;

I fully believe that Git and Mercurial is equally powerful. Their
internal concepts are very, very similar. You can map between the tools
in a nearly loss-less way (see the hg-git extension).

To me, arguing that Git is more powerful since it exposes more commands
by default ('git rebase -i' is the typical example) is like arguing that
Perl is more powerful than Python since Perl has a built-in regex
operator -- we all know that both languages are Turing complete.

> - they are built with very different architectures (many executables
>   written in C versus a monolithic program in Python), but in the end
>   both work well enough and both seem extensible enough for most
>   purposes.

Both are great tools and both will work well for a big and complex
project like Boost.

Mercurial has some new features which isn't found in other systems:

- Revision sets: a query language that lets you select commits. An
  example from [1] is

    hg log -r "1.3::1.5 and keyword(bug) and file('hgext/*')"

  This syntax can be used with all commands that take a -r flag.

- File sets: similar to revsets, but for selecting files. An example
  from [2] would be

    hg revert "set:copied() and binary() and size('>1M')"

  I think formulating the equivalent query with find(1) would be hard.

- Heavy-weight branches: Mercurial has named branches which are built
  into the changesets. This lets you track exactly where a branch
  started and where it ended. These branches are very *different* from
  branches in Git: they are permanent and global. In this way, named
  branches are much more similar to branches in CVS and SVN.

  The closest equivalent of Git's branch model is called bookmarks in
  Mercurial. See the glossary[3].

[1]: http://www.selenic.com/mercurial/hg.1.html#revset
[2]: http://www.selenic.com/mercurial/hg.1.html#fileset
[3]: http://www.selenic.com/mercurial/hg.1.html#glossary

-- 
Martin Geisler
Professional Mercurial support by aragost Trifork
http://www.aragost.com/mercurial/