using fstring = xtl::xfixed_string<55>;

using data_type = xt::xoptional_assembly<xt::xarray<double>, xt::xarray<bool>>;
using coordinate_type = xf::xcoordinate<fstring, data_type::size_type>;

using variable_type = xf::xvariable<coordinate_type, data_type>;
using variable_view_type = xf::xvariable_view<variable_type&>;
using saxis_type = xf::xaxis<fstring, std::size_t>; 
using iaxis_type = xf::xaxis<int, std::size_t>;

fstring abscissa = "abscissa";
fstring ordinate = "ordinate";

// Shape 3x3
data_type data1 = {{ 1., 2., 3.},
                  { 4., 5., 6.},
                  { 7., 8., 9.}};

// Shape 1x3 for the coordinates
auto var1 = variable_type(
    data1,
    {
        {abscissa, saxis_type({"a"})},
        {ordinate, iaxis_type({1, 2, 4})}
    }
);