adjoint_of.hpp

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#ifndef STAN_MATH_REV_FUN_ADJOINT_OF_HPP
#define STAN_MATH_REV_FUN_ADJOINT_OF_HPP
 
#include <stan/math/rev/core.hpp>
 
namespace stan {
namespace math {
 
namespace internal {
struct nonexisting_adjoint {
  template <typename T>
  nonexisting_adjoint operator+(const T&) {
    return *this;
  }
  template <typename T>
  nonexisting_adjoint operator+=(T) const {
    throw std::runtime_error(
        "internal::nonexisting_adjoint::operator+= should never be called! "
        "Please file a bug report. rev/fun/adjoint_of.hpp line "
        + std::to_string(__LINE__));
  }
  template <typename T>
  nonexisting_adjoint operator-=(T) const {
    throw std::runtime_error(
        "internal::nonexisting_adjoint::operator-= should never be called! "
        "Please file a bug report. rev/fun/adjoint_of.hpp line "
        + std::to_string(__LINE__));
  }
};
}  // namespace internal
 
template <typename T, require_var_t<T>* = nullptr>
inline auto& adjoint_of(const T& x) noexcept {
  return x.adj();
}
 
template <typename T, require_not_var_t<T>* = nullptr>
internal::nonexisting_adjoint adjoint_of(const T& x) {
  return {};
}
 
}  // namespace math
}  // namespace stan
 
#endif  // ADJOINT_OF_HPP