boost::histogram::axis::traits::is_continuous — Whether axis is continuous or discrete.
// In header: <boost/histogram/axis/traits.hpp> template<typename Axis> struct is_continuous { };
Doxygen does not render this well. This is a meta-function (template alias), it accepts an axis type and returns a compile-time boolean.
If the boolean is true, the axis is continuous (covers a continuous range of values). Otherwise it is discrete (covers discrete values).