enumerator value "None" in the "simdize.h" header file of Vc conflicts with the preprocessor macro "None" defined in the X11 header file "X.h"

[dkonst13]

During compilation of Geant4 visualization/OpenGL/src/G4OpenGLImmediateXViewer.cc, I encountered an error. It seems that the enumerator value "None" in the "simdize.h" header file of Vc conflicts with the preprocessor macro "None" defined in the X11 header file "X.h".

/usr/include/X11/X.h:

#ifndef None
#define None                 0L /* universal null resource or null atom */
#endif

And include/Vc/common/simdize.h:

enum class Category {
    ///\internal No transformation
    None,
    ///\internal simple Vector<T> transformation
    ArithmeticVectorizable,
    ///\internal transform an input iterator to return vectorized entries
    InputIterator,
    ///\internal transform a forward iterator to return vectorized entries
    OutputIterator,
    ///\internal transform an output iterator to return vectorized entries
    ForwardIterator,
    ///\internal transform a bidirectional iterator to return vectorized entries
    BidirectionalIterator,
    ///\internal transform a random access iterator to return vectorized entries
    RandomAccessIterator,
    ///\internal transform a class template recursively
    ClassTemplate
};

It would be nice if this can be fixed...

Thank you!

[bernhardmgruber]

Since the concerning enumerator is an internal name of the Vc library, I don't see a big concern renaming it. Alternatively, we can also #undef the macro like we do with some other macro's as well: https://github.com/VcDevel/Vc/blob/1.4/Vc/common/macros.h#L47-L55