Maybe you know this, but let me explain this. Names begin with an underscore followed by an uppercase letter are reserved to compilers for any use (C++ Standard §17.4.3.1.2). So it is unsafe to use template parameter's name like _Scalar, _Rows, etc. How about changing these names to Scalar_, Rows_, …?
We know this, and we don't really care until we actually run into a collision. Let us know if you have.
I didn't have any problem with this. So it may be unnecessary concern.
Bug 658 is an example for a collision. I would vote for changing all possibly colliding names (even though some are unlikely to be used by a compiler).
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