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//                        Kokkos v. 2.0
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// Experimental unified task-data parallel manycore LDRD

#ifndef KOKKOS_IMPL_OPTIONALREF_HPP
#define KOKKOS_IMPL_OPTIONALREF_HPP

#include <Kokkos_Macros.hpp>

#include <Kokkos_Core_fwd.hpp>

#include <Kokkos_PointerOwnership.hpp>
#include <impl/Kokkos_Error.hpp>

//----------------------------------------------------------------------------
//----------------------------------------------------------------------------
namespace Kokkos {
namespace Impl {

struct InPlaceTag { };

template <class T>
struct OptionalRef {
private:

  ObservingRawPtr<T> m_value = nullptr;

public:

  using value_type = T;

  KOKKOS_INLINE_FUNCTION
  OptionalRef() = default;

  KOKKOS_INLINE_FUNCTION
  OptionalRef(OptionalRef const&) = default;
  
  KOKKOS_INLINE_FUNCTION
  OptionalRef(OptionalRef&&) = default;

  KOKKOS_INLINE_FUNCTION
  OptionalRef& operator=(OptionalRef const&) = default;

  KOKKOS_INLINE_FUNCTION
  // Can't return a reference to volatile OptionalRef, since GCC issues a warning about
  // reference to volatile not accessing the underlying value
  void
  operator=(OptionalRef const volatile& other) volatile noexcept
  {
    m_value = other.m_value;
  }

  KOKKOS_INLINE_FUNCTION
  OptionalRef& operator=(OptionalRef&&) = default;

  KOKKOS_INLINE_FUNCTION
  ~OptionalRef() = default;

  KOKKOS_INLINE_FUNCTION
  explicit OptionalRef(T& arg_value) : m_value(&arg_value) { }

  KOKKOS_INLINE_FUNCTION
  explicit OptionalRef(std::nullptr_t) : m_value(nullptr) { }

  KOKKOS_INLINE_FUNCTION
  OptionalRef& operator=(T& arg_value) { m_value = &arg_value; return *this; }

  KOKKOS_INLINE_FUNCTION
  OptionalRef& operator=(std::nullptr_t) { m_value = nullptr; return *this; }

  //----------------------------------------

  KOKKOS_INLINE_FUNCTION
  OptionalRef<typename std::add_volatile<T>::type>
  as_volatile() volatile noexcept {
    return 
      OptionalRef<typename std::add_volatile<T>::type>(*(*this));
  }

  KOKKOS_INLINE_FUNCTION
  OptionalRef<typename std::add_volatile<typename std::add_const<T>::type>::type>
  as_volatile() const volatile noexcept {
    return 
      OptionalRef<typename std::add_volatile<typename std::add_const<T>::type>::type>(*(*this));
  }


  //----------------------------------------

  KOKKOS_INLINE_FUNCTION
  T& operator*() & {
    KOKKOS_EXPECTS(this->has_value());
    return *m_value;
  }
   
  KOKKOS_INLINE_FUNCTION
  T const& operator*() const & {
    KOKKOS_EXPECTS(this->has_value());
    return *m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T volatile& operator*() volatile & {
    KOKKOS_EXPECTS(this->has_value());
    return *m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T const volatile& operator*() const volatile & {
    KOKKOS_EXPECTS(this->has_value());
    return *m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T&& operator*() && {
    KOKKOS_EXPECTS(this->has_value());
    return std::move(*m_value);
  }

  KOKKOS_INLINE_FUNCTION
  T* operator->() {
    KOKKOS_EXPECTS(this->has_value());
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T const* operator->() const {
    KOKKOS_EXPECTS(this->has_value());
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T volatile* operator->() volatile {
    KOKKOS_EXPECTS(this->has_value());
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T const volatile* operator->() const volatile {
    KOKKOS_EXPECTS(this->has_value());
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T* get() {
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T const* get() const {
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T volatile* get() volatile {
    return m_value;
  }

  KOKKOS_INLINE_FUNCTION
  T const volatile* get() const volatile {
    return m_value;
  }

  //----------------------------------------

  KOKKOS_INLINE_FUNCTION
  operator bool() { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  operator bool() const { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  operator bool() volatile { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  operator bool() const volatile { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  bool has_value() { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  bool has_value() const { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  bool has_value() volatile { return m_value != nullptr; }

  KOKKOS_INLINE_FUNCTION
  bool has_value() const volatile { return m_value != nullptr; }
  
};

} // end namespace Impl
} // end namespace Kokkos

//----------------------------------------------------------------------------
//----------------------------------------------------------------------------



#endif /* #ifndef KOKKOS_IMPL_OPTIONALREF_HPP */

