Re: [eigen] Eigen2 to Eigen3 Migration Path

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

2011/1/14 Tully Foote <tfoote@xxxxxxxxxxxxxxxx>:
>
>
> On 01/13/2011 09:06 PM, Benoit Jacob wrote:
>
> 2011/1/13 Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>:
>
> On Thu, Jan 13, 2011 at 12:13 AM, Gael Guennebaud
> <gael.guennebaud@xxxxxxxxx> wrote:
>
> 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.
>
> 3 - lib B is a binary library without Eigen2 in the public API. Again, there
> exists the possibility to recombile B with Eigen3+EIGEN2_SUPPORT.
>
> Asumming for a moment we had Eigen:: and Eigen3:: namespaces. This would
> imply the following things.
>
> OK, so let's focus for now on Gael's solution (tell people to use
> Eigen3 + EIGEN2_SUPPORT) plus my suggestion to make EIGEN2_SUPPORT as
> complete as possible and validated by the actual eigen2 test suite. At
> least it doesn't hurt anyone.
>
> It's true that if Eigen3 + EIGEN2_SUPPORT were 100% API compatible
> with Eigen2 then the lack of ABI compatibility wouldn't be a big
> problem anymore since switching would be virtually costless.
>
> I believe that if we do have full coverage of the Eigen2 API with
> Eigen3+EIGEN2_SUPPORT this would be fine for our use cases.  We would just
> compile all libraries against EIgen3+EIGEN2_SUPPORT instead of Eigen2.
>
> Tully
>
>  Regarding kdl (http://www.orocos.org/kdl), I tried to compile it
> against Eigen3+EIGEN2_SUPPORT and the major hickup I am seeing is caused by
> Map's const-correctness. We should be able to fix that through the plugin by
> re-enabling the non-const constructor of Maps though I did not properly
> think this over.
>
> Ah, ok. It should be quite easy to allow non-const-correct Map
> constructors with EIGEN2_SUPPORT.

Great to see a solution on the horizon. Now we need to implement it. I
filed a bug:

http://eigen.tuxfamily.org/bz/show_bug.cgi?id=153

I marked it as blocking 3.0, as it doesn't really need to be tested in
a beta. Could even not block 3.0 actually, but I have a feeling that
that can be implemented quickly.

Benoit