Re: [eigen] Eigen2 to Eigen3 Migration Path

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2011/1/12 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
> I have to say that I'm not fan of such a change, and I would feel very
> uncomfortable to ask to all users that I encouraged to directly (or
> move to) Eigen3 to have to do such a change. Also this implies that
> everybody update their Eigen3 copy and their libs at the same time...

The reason why this discussion is difficult seems to be that this
time, we can't please everybody: current eigen3 users, and eigen2
users moving to eigen3. My point of view was that the burden I was
talking of putting onto current eigen3 users wasn't such a big deal,
since it's just search and replace.

>
> I'm also not sure what is the point of mixing Eigen2 and Eigen3 in the
> same project since Eigen 2 and 3 objects are not compatible anyway.

A single project might use Eigen2 and Eigen3 for separate tasks... I
don't think anyone is saying that this is a good idea, it was just
brought up as an inevitable state of transition as people move large
projects to eigen3.

>
> The EIGEN2_SUPPORT way seems much more powerful. Let's be specific. If
> project A wants to use Eigen3 as well as a lib B which relies on
> Eigen2 then there are two cases:
> 1 - lib B is a pure template lib (or at least the parts which rely on
> Eigen2) then EIGEN2_SUPPORT should do the job (we can make it better
> if needed).
> 2 - lib B is a binary library with a public API involving Eigen2
> objects. Then there is still the possibility to recompile B with
> Eigen3+EIGEN2_SUPPORT.

That's a good point. But my understanding was that Tully's point was
that in a large project, even an ecosystem, there may not exist a
single actor who can single-handedly recompile everything, so that's
hard to synchronize too.

We probably should give ourselves a few more days of thought to come
up with a solution that doesn't hurt anybody...

Cheers
Benoit


>
> gael
>
> On Wed, Jan 12, 2011 at 10:24 PM, Hauke Heibel
> <hauke.heibel@xxxxxxxxxxxxxx> wrote:
>> On Wed, Jan 12, 2011 at 9:48 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
>> wrote:
>>>
>>> Tully's concern is much more serious than that! There is the concern
>>> of having Eigen2 and Eigen3 coexist in a single software project,
>>> which as discussed is going to stay the case for some time as
>>> libraries using Eigen2 port to Eigen3.
>>
>> Ok, it seems to be all about being able to let Eigen2 and Eigen3 and maybe
>> EigenX co-exist. I am fine with that, if that is really what you want to
>> support.
>> That I am not a fan of this feature is probably a matter of taste. I am
>> already thinking of requests such as being able to convert an
>> Eigen2::MatrixXf to an Eigen3::MatrixXf.
>> - Hauke
>>
>
>
>