cuda_toolkit/include/__mdspan/no_unique_address.h

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#ifndef _LIBCUDACXX__LIBCUDACXX_NO_UNIQUE_ADDRESS_HPP
#define _LIBCUDACXX__LIBCUDACXX_NO_UNIQUE_ADDRESS_HPP

#ifndef __cuda_std__
#include <__config>
#endif // __cuda_std__

#include "../__mdspan/macros.h"
#include "../__type_traits/enable_if.h"
#include "../__type_traits/is_empty.h"
#include "../__type_traits/is_trivially_destructible.h"
#include "../__utility/move.h"

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

_LIBCUDACXX_BEGIN_NAMESPACE_STD

#if _LIBCUDACXX_STD_VER > 11

namespace __detail {

//==============================================================================

template <class _Tp, size_t _Disambiguator = 0, class _Enable = void>
struct __no_unique_address_emulation {
  using __stored_type = _Tp;
  _Tp __v;
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp const &__ref() const noexcept {
    return __v;
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp &__ref() noexcept {
    return __v;
  }
};

// Empty case
// This doesn't work if _Tp is final, of course, but we're not using anything
// like that currently. That kind of thing could be added pretty easily though
template <class _Tp, size_t _Disambiguator>
struct __no_unique_address_emulation<
    _Tp, _Disambiguator,
    _CUDA_VSTD::enable_if_t<_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_empty, _Tp) &&
                // If the type isn't trivially destructible, its destructor
                // won't be called at the right time, so don't use this
                // specialization
                _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_trivially_destructible, _Tp)>> :
#ifdef __MDSPAN_COMPILER_MSVC
    // MSVC doesn't allow you to access public static member functions of a type
    // when you *happen* to privately inherit from that type.
    protected
#else
    // But we still want this to be private if possible so that we don't accidentally
    // access members of _Tp directly rather than calling __ref() first, which wouldn't
    // work if _Tp happens to be stateful and thus we're using the unspecialized definition
    // of __no_unique_address_emulation above.
    private
#endif
    _Tp {
  using __stored_type = _Tp;
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp const &__ref() const noexcept {
    return *static_cast<_Tp const *>(this);
  }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr _Tp &__ref() noexcept {
    return *static_cast<_Tp *>(this);
  }

  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __no_unique_address_emulation() noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __no_unique_address_emulation(
      __no_unique_address_emulation const &) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  constexpr __no_unique_address_emulation(
      __no_unique_address_emulation &&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __no_unique_address_emulation &
  operator=(__no_unique_address_emulation const &) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  __MDSPAN_CONSTEXPR_14_DEFAULTED __no_unique_address_emulation &
  operator=(__no_unique_address_emulation &&) noexcept = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  ~__no_unique_address_emulation() noexcept = default;

  // Explicitly make this not a reference so that the copy or move
  // constructor still gets called.
  __MDSPAN_INLINE_FUNCTION
  explicit constexpr __no_unique_address_emulation(_Tp const& __v) noexcept : _Tp(__v) {}
  __MDSPAN_INLINE_FUNCTION
  explicit constexpr __no_unique_address_emulation(_Tp&& __v) noexcept : _Tp(_CUDA_VSTD::move(__v)) {}
};

//==============================================================================

} // end namespace __detail

#endif // _LIBCUDACXX_STD_VER > 11

_LIBCUDACXX_END_NAMESPACE_STD

#endif // _LIBCUDACXX__LIBCUDACXX_NO_UNIQUE_ADDRESS_HPP