[eigen] Subject: why are AutoDiff to value conversions disabled?

[Geoffrey Lalonde <glalonde@xxxxxx>]

See the conversions commented out here: https://bitbucket.org/eigen/eigen/src/df279134beee3771e025160762e976680de90503/unsupported/Eigen/src/AutoDiff/AutoDiffScalar.h?at=default&fileviewer=file-view-default#AutoDiffScalar.h-149

Is there a good reason for this? I often find myself writing functions templated for both real scalars scalar or autodiff scalars, and if I want to read the real scalar value out of this templated code, I need to jump through some hoops that could be avoided by just using a static_cast<double>(maybe_autodiff_scalar) if these lines were uncommented.

Alternatively, is it possible to enable this conversion externally without modifying eigen's source but to still have it as work as transparently?

Thanks,

Geoff