template <typename RefType>
  class Optional
  {
  public:
    Optional( RefType & reference ) VULKAN_HPP_NOEXCEPT
    {
      m_ptr = &reference;
    }
    Optional( RefType * ptr ) VULKAN_HPP_NOEXCEPT
    {
      m_ptr = ptr;
    }
    Optional( std::nullptr_t ) VULKAN_HPP_NOEXCEPT
    {
      m_ptr = nullptr;
    }

    operator RefType *() const VULKAN_HPP_NOEXCEPT
    {
      return m_ptr;
    }
    RefType const * operator->() const VULKAN_HPP_NOEXCEPT
    {
      return m_ptr;
    }
    explicit operator bool() const VULKAN_HPP_NOEXCEPT
    {
      return !!m_ptr;
    }

  private:
    RefType * m_ptr;
  };