Re: [eigen] Eigen2 to Eigen3 Migration Path

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

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.

> 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.

Benoit