KokkosReferenceWrapper.h

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//* This file is part of the MOOSE framework
//* https://www.mooseframework.org
//*
//* All rights reserved, see COPYRIGHT for full restrictions
//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
//*
//* Licensed under LGPL 2.1, please see LICENSE for details
//* https://www.gnu.org/licenses/lgpl-2.1.html

#pragma once

#include "KokkosArray.h"

#include "MooseTypes.h"

namespace Moose::Kokkos
{

template <typename T>
class ReferenceWrapper
{
public:
  ReferenceWrapper(T & reference) : _reference(reference), _copy(reference) {}
  ReferenceWrapper(const ReferenceWrapper<T> & object)
    : _reference(object._reference), _copy(object._reference)
  {
  }

#ifdef MOOSE_KOKKOS_SCOPE

  KOKKOS_FUNCTION operator const T &() const
  {
    KOKKOS_IF_ON_HOST(return _reference;)

    return _copy;
  }
  KOKKOS_FUNCTION const T & operator*() const
  {
    KOKKOS_IF_ON_HOST(return _reference;)

    return _copy;
  }
  KOKKOS_FUNCTION const T * operator->() const
  {
    KOKKOS_IF_ON_HOST(return &_reference;)

    return &_copy;
  }
  template <typename... Args>
  KOKKOS_FUNCTION auto operator()(Args &&... args) const -> decltype(auto)
  {
    KOKKOS_IF_ON_HOST(return _reference(std::forward<Args>(args)...);)

    return _copy(std::forward<Args>(args)...);
  }
#else

  operator const T &() const { return _reference; }
  const T & operator*() const { return _reference; }
  const T * operator->() const { return &_reference; }
  template <typename... Args>
  auto operator()(Args &&... args) const -> decltype(auto)
  {
    return _reference(std::forward<Args>(args)...);
  }
#endif

  operator T &() { return _reference; }
  T & operator*() { return _reference; }
  T * operator->() { return &_reference; }
  template <typename... Args>
  auto operator()(Args &&... args) -> decltype(auto)
  {
    return _reference(std::forward<Args>(args)...);
  }

protected:
  T & _reference;
  const T _copy;
};

template <typename T>
struct ArrayDeepCopy<ReferenceWrapper<T>>
{
  static constexpr bool value = true;
};

} // namespace Moose::Kokkos