[eigen] Eigen in a namespace?

[Robert Lupton the Good <rhl@xxxxxxxxxxxxxxxxxxx>]

We've been using eigen (at a lowish level) for quite a time in a large astronomical software project, the LSST, and now have the desire to include a semi-external package;  both use eigen.

For packaging reasons the semi-external package would like to include its own copy of the eigen headers (probably as a sub-module from git), so we potentially have two copies of eigen in the same dynamically-loaded package (both imported into python).  We're worried about ABI/API issues as eigen evolves in interesting ways.

One way to fix this would be to include eigen in different namespaces (maybe anonymous?) in the two packages, but I don't think that this is possible due to eigen's use of the STL.  Is there any way to do this now?  Or alternatively would it be crazy to restructure the eigen includes to allow us to include a header outside our namespace that pulls in the STL, and then the "real" eigen headers inside our namespace?

						R

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