Copy semantic consistency not match the documents

[blknit]

When I study xtensor with document https://xtensor.readthedocs.io/en/latest/scalar.html
The result of the following code not match the document, it is the same as result in "Assignment"
So there no different between assign and copy constructor?

`#include <xtensor/xarray.hpp>

xt::xarray a = {{0., 1., 2.}, {3., 4., 5.}};
double s = 1.2;
a = 1.2;
std::cout << a << std::endl;
// prints {{1.2, 1.2, 1.2}, {1.2, 1.2, 1.2}}
`