OpenMC/tests/regression_tests/source_parameterized_dlopen/parameterized_source_sampling.cpp

#include "openmc/particle_data.h"
#include "openmc/source.h"

class CustomSource : public openmc::Source {
public:
  CustomSource(double energy) : energy_(energy) {}

  // Samples from an instance of this class.
  openmc::SourceSite sample(uint64_t* seed) const
  {
    openmc::SourceSite particle;
    // wgt
    particle.particle = openmc::ParticleType::neutron();
    particle.wgt = 1.0;
    // position
    particle.r.x = 0.0;
    particle.r.y = 0.0;
    particle.r.z = 0.0;
    // angle
    particle.u = {1.0, 0.0, 0.0};
    particle.E = this->energy_;
    particle.delayed_group = 0;

    return particle;
  }

private:
  double energy_;
};

// A function to create a unique pointer to an instance of this class when
// generated via a plugin call using dlopen/dlsym. You must have external C
// linkage here otherwise dlopen will not find the file
extern "C" std::unique_ptr<CustomSource> openmc_create_source(
  std::string parameter)
{
  double energy = std::stod(parameter);
  return std::make_unique<CustomSource>(energy);
}