(libtorch) Problem saving cpp model

I’m trying to use libtorch to create and save models. Following the DCGAN tutorial and this I create a basic script as given here

class TestImpl: torch::nn::Module
  TestImpl(int inPlanes, int outClasses)
    : m_score(torch::nn::Conv2dOptions(inPlanes, outClasses, 1))
  double forward(at::Tensor& input, at::Tensor& output)
    auto start = std::chrono::system_clock::now();

    output = m_score->forward(input);

    auto end = std::chrono::system_clock::now();
    std::chrono::duration<double> elapsed_seconds = end-start;
    return double(elapsed_seconds.count());
  torch::nn::Conv2d m_score{nullptr};

int main(int argc, char** argv )
  Test net(3,10);
  int loop = 100;
  int skip = 20;
  float timing;
  at::Tensor outputs;
  at::Tensor inputs = torch::ones({1, 3, 1024, 1024},torch::TensorOptions().device(torch::kCUDA));

  for (auto i = 0; i < loop+skip; i++)
      auto tmp = net->forward(inputs, outputs);//_pass(inputs, outputs);

      if(i >= skip)
          timing += tmp;
  std::cout<< "Average forward pass in: " << timing/loop <<std::endl;
  torch::save(net, "chkValues.pt");

When I comment out the last line (torch::save) it compiles fine but un-commenting this throws out a lot of errors starting with:

In file included from libtorch_stable/include/torch/csrc/api/include/torch/nn/module.h:3:0,
                 from libtorch_stable/include/torch/csrc/api/include/torch/nn/cloneable.h:3,
                 from libtorch_stable/include/torch/csrc/api/include/torch/nn.h:3,
                 from libtorch_stable/include/torch/csrc/api/include/torch/all.h:7,
                 from timing.cpp:36:
libtorch_stable/include/torch/csrc/api/include/torch/nn/pimpl.h: In instantiation of ‘torch::serialize::OutputArchive& torch::nn::operator<<(torch::serialize::OutputArchive&, const torch::nn::ModuleHolder<ModuleType>&) [with ModuleType = TestImpl]’:
libtorch_stable/include/torch/csrc/api/include/torch/serialize.h:43:11:   required from ‘void torch::save(const Value&, SaveToArgs&& ...) [with Value = Test; SaveToArgs = {const char (&)[13]}]’
timing.cpp:127:34:   required from here
libtorch_stable/include/torch/csrc/api/include/torch/nn/pimpl.h:179:18: error: no match for ‘operator<<’ (operand types are ‘torch::serialize::OutputArchive’ and ‘const std::shared_ptr<TestImpl>’)
   return archive << module.ptr();

Could someone please help me understand why this is happening?
I’m using libtorch-stable 1.4 version with cuda 9.2.

Replying to my question… it looks like replacing class TestImpl with struct TestImpl things work fine. Not sure why this is the case.