reverse_pass_callback.hpp

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#ifndef STAN_MATH_REV_FUNCTOR_REVERSE_PASS_CALLBACK_HPP
#define STAN_MATH_REV_FUNCTOR_REVERSE_PASS_CALLBACK_HPP
 
#include <stan/math/rev/core/vari.hpp>
#include <new>
 
namespace stan {
namespace math {
namespace internal {
 
template <typename F>
struct reverse_pass_callback_vari : public vari_base {
  F rev_functor_;
 
  STAN_STRONG_INLINE STAN_HOT_PATH explicit reverse_pass_callback_vari(
      F&& rev_functor)
      : rev_functor_(std::forward<F>(rev_functor)) {
    ChainableStack::instance_->push_var_stack(this);
  }
 
  inline void chain() final { rev_functor_(); }
  inline void set_zero_adjoint() final {}
  inline void init_dependent() {}
};
 
}  // namespace internal
 
template <typename F>
STAN_STRONG_INLINE STAN_HOT_PATH void reverse_pass_callback(F&& functor) {
  // Captures such as fixed-size Eigen matrices can need more than the 8 byte
  // alignment of `vari_base::operator new`.
  using vari_t = internal::reverse_pass_callback_vari<F>;
  ::new (ChainableStack::instance_->memalloc_.alloc(
      sizeof(vari_t), alignof(vari_t))) vari_t(std::forward<F>(functor));
}
 
}  // namespace math
}  // namespace stan
 
#endif