After seeing the example of xtensor matrix adaptors of 1D containers, I was wondering if it is also possible to have a resizeable adaptor of STL containers like vectors.

In the process, I would like to also find out and use the type of such an adaptor, instead of using auto.

Starting with the C-style array adaptor and compute() function –which multiplies the 2×1 row vector with a 2×1 column and returns the xarray as a 2×2 matrix– I got as far as

using shape_type    = std::vector < size_t >;
using adaptor_typev = xt::xarray_adaptor < xt::xbuffer_adaptor < double*,            
                                                                 xt::acquire_ownership >, 
                                           xt::layout_type::dynamic, 
                                           shape_type >;

unsigned                    vsize    = 2;
std::vector < double >      vdata    = { 0, 1 };
std::vector < std::size_t > vshape   = { vsize };
std::vector < std::size_t > vstrides = { 1 };

adaptor_typev 
    my_adaptorv = xt::adapt ( vdata.data(), 
                              vsize, 
                              xt::acquire_ownership(), 
                              vshape, 
                              vstrides);

std::cout << "n";  
std::cout << "nbefore reshapen";
for ( unsigned i = 0; i < vsize; i++ )
    std::cout << vdata [ i ] << " ";

compute ( my_adaptorv );

std::cout << "nafter reshapen";
for ( unsigned i = 0; i < vsize * vsize; i++ )
    std::cout << vdata [ i ] << " ";

The output that I get from the C-style xarray_adaptor (from the xtensor website) and the std:vector xarray_adaptor, respectively, is:

before reshape
0 1
after reshape
0 1 0 2

before reshape
0 1
after reshape
0 1 nan -5.11336e-311

==== Program exited with exit code: 3221226356 ====
Time elapsed: 000:00.016 (MM:SS.MS)

The last two values suggest that the resize has not happened, and the non-zero exit code shows all is not well. If I run it in the debugger, it exits with a SIGTRAP at the end of main(). The top of the call stack says ntdll!RtllsZeroMemory.

Does that mean that to resize an xarray adaptor of an std::vector, I need to resize the vector separately? Or is there a way to do it without trying to become owner of the vector’s data (that does not sound right to begin with)?