assigning a view values from another view

[hassanromhuda]

I'm expecting that the code below should work, but it doesn't compile.

int main(int argc, char** argv) {
  auto a = xt::arange(10);
  auto a_view = xt::reshape_view(a, {1, 5, 2});

  auto b_view = xt::view(a_view, xt::all(), xt::range(3, 5), xt::all());
  auto c_view = xt::view(a_view, xt::all(), xt::range(1, 3), xt::all());

  c_view = b_view;

  return 0;
}

The compilation error I'm getting:

examples/xtensor_main.cc:14:12:   required from here
bazel-out/k8-fastbuild/bin/external/xtensor/_virtual_includes/xtensor/xtensor/xstrided_view.hpp:478:16: error: no matching function for call to 'xt::xindexed_stepper<xt::xstrided_view<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, std::array<long unsigned int, 3>, xt::layout_type::dynamic, xt::detail::flat_adaptor_getter<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, xt::layout_type::row_major> >, false>::xindexed_stepper(xt::xstrided_view<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, std::array<long unsigned int, 3>, xt::layout_type::dynamic, xt::detail::flat_adaptor_getter<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, xt::layout_type::row_major> >*, xt::xstrided_view<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, std::array<long unsigned int, 3>, xt::layout_type::dynamic, xt::detail::flat_adaptor_getter<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, xt::layout_type::row_major> >::container_iterator, xt::xstrided_view<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, std::array<long unsigned int, 3>, xt::layout_type::dynamic, xt::detail::flat_adaptor_getter<xt::xgenerator<xt::detail::arange_generator<int, int, int>, int, std::array<long unsigned int, 1> >&, xt::layout_type::row_major> >::size_type&)'
  478 |         return stepper(this, data_xbegin(), offset);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`

Any ideas or temporary workarounds?

[JohanMabille]

As stated in https://xtensor.readthedocs.io/en/latest/builder.html#expression-builders, arange returns a lazy expression, holding no value. Therefore, you cannot assign to it, or to view on it, you need to evaluate it first:

auto avalue = xt::eval(a_view).
auto b_view = xt::view(avalue, xt::all(), xt::range(3, 5), xt::all());
auto c_view = xt::view(avalue, xt::all(), xt::range(1, 3), xt::all());

[github-actions]

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