OpenMC/tests/regression_tests/source_parameterized_dlopen/parameterized_source_sampling.cpp

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

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

    // Samples from an instance of this class.
    openmc::Particle::Bank sample(uint64_t* seed) const
    {
      openmc::Particle::Bank particle;
      // wgt
      particle.particle = openmc::Particle::Type::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);
}