parameter to constexpr function cannot be used as constant
This is related to issue #1 (closed)
One cannot use a parameter as argument to constexpr function within (and also outside) a non-evaluated context. Although GCC accepts it, other compilers, e.g. intel icc 18, throw an errror.
A second issue is corrected: (with intel compiler) one can not simply pass an instantiated
std::integral_constant to an
enable_if as condition argument. Also, the template alias
is_flat_index is not found in a sub-namespace for some reasons.