[eigen] Re: introducing the Eigen2 support stages

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

A little update:

the stage 2, RESOLVE_API_CONFLICTS, is now producing errors instead of
warnings, to help make sure that these very important issues are
caught.

a new stage "1.5" has been introduced, doing what stage 2 used to do
(produce warnings). it's called RESOLVE_API_CONFLICTS_WARN.

So i've multiplied all the constants by 10 to make room. The stages
currently are:

EIGEN2_SUPPORT_STAGE10_FULL_EIGEN2_API
EIGEN2_SUPPORT_STAGE15_RESOLVE_API_CONFLICTS_WARN
EIGEN2_SUPPORT_STAGE20_RESOLVE_API_CONFLICTS
EIGEN2_SUPPORT_STAGE30_FULL_EIGEN3_API
EIGEN2_SUPPORT_STAGE40_FULL_EIGEN3_STRICTNESS

On the implementation front, almost all the core functionality is
passing, but the 'triangular' test, covering things such as part(),
took me longer than anticipated. I still hope that by tomorrow I
should be almost done.

Benoit

2011/1/21 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
> Hi,
>
> As you may know, we are in the process of making the transition from
> eigen2 to 3 as easy as possible by making the EIGEN2_SUPPORT mode
> fully Eigen2 API compatible.
>
> However, as was discussed, there are a few corner cases where this is
> impossible, because eigen2 and 3 use different conventions for the
> same API.
>
> So it's been suggested to split EIGEN2_SUPPORT into multiple 'stages',
> and I have just dmplemented that.
>
> First of all, if you are currently doing #define EIGEN2_SUPPORT, don't
> worry: it stays supported, nothing changes. It just becomes a shortcut
> for what I'll call below "stage 3"
>
> So here are the different stages:
>
> 1)  #define EIGEN2_SUPPORT_STAGE1_FULL_EIGEN2_API
>
> When you #define this before including Eigen3 headers, you get 100%
> support of the Eigen2 API (once ongoing work is completed), so that
> Eigen2-using code compiles unchanged.
>
> That means that when a convention is different between eigen2 and
> eigen3, the eigen2 convention is used. For example, for complex
> vectors x and y,  x.dot(y)  conjugates y (dot product linear in the
> first variable x).
>
> For such cases where the eigen2 and eigen3 APIs conflict, we introduce
> eigen2_ prefixed functions, so you can replace
>  x.dot(y)
> by
>  x.eigen2_dot(y)
>
> 2)  #define EIGEN2_SUPPORT_STAGE2_RESOLVE_API_CONFLICTS
>
> This is identical to stage 1 except that the eigen2 API that conflicts
> with eigen3 is now deprecated. So when you do
>  x.dot(y)
> you get a 'deprecated' warning even though that would also compile in
> pure eigen3 (but with a different meaning). At this stage, you should
> go over these warnings and fix them by using eigen2_ prefixed
> functions:
>  x.eigen2_dot(y)
>
> 3) #define EIGEN2_SUPPORT_STAGE3_FULL_EIGEN3_API
>
> This is what you get when you just #define EIGEN_SUPPORT.
> This stage switches to eigen3 conventions everywhere. So now x.dot(y)
> is linear in the first variable. You may still use eigen2_ prefixed
> functions, and of course the rest of the Eigen2 API is still available
> unchanged.
>
> Also, where Eigen2 allows to do const-incorrect things (such as
> mapping const data as non-const Map), this stage still allows it.
>
> 4) #define EIGEN2_SUPPORT_STAGE4_FULL_EIGEN3_STRICTNESS
>
> This stage enables eigen3 strictness where eigen2 was laxist. In
> particular, it enforces const-correctness of Map.
>
> Notice that making the EIGEN2_SUPPORT_STAGE1_FULL_EIGEN2_API mode 100%
> API compatible is work in progress. I am still in the process of
> making the eigen2 test suite succeed. I'd say it should be completed
> during this weekend.
>
> Of course, I expect most small projects to just us EIGEN2_SUPPORT
> (which, again, is giving you stage 3) and not worry about this at all.
>
> Of course, this needs to be explained in the online 'porting from
> eigen 2 to eigen3' dox page.
>
> Benoit
>