BSTSmartPointer.h

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#pragma once
 
namespace RE
{
    template <class T>
    struct BSTSmartPointerIntrusiveRefCount
    {
        static void Acquire(T* a_ptr)
        {
            a_ptr->IncRef();
        }
 
        static void Release(T* a_ptr)
        {
            if (a_ptr->DecRef() == 0) {
                delete a_ptr;
            }
        }
    };
 
    template <class T>
    struct BSTSmartPointerAutoPtr
    {
        constexpr static void Acquire(T* a_ptr)
        {
            return;
        }
 
        static void Release(T* a_ptr)
        {
            delete a_ptr;
        }
    };
 
    template <class T, template <class> class RefManager = BSTSmartPointerIntrusiveRefCount>
    class BSTSmartPointer
    {
    public:
        using element_type = T;
        using reference_manager = RefManager<T>;
 
        // 1
        inline constexpr BSTSmartPointer() noexcept :
            _ptr(nullptr)
        {}
 
        // 2
        inline constexpr BSTSmartPointer(std::nullptr_t) noexcept :
            _ptr(nullptr)
        {}
 
        // 3
        template <
            class Y,
            std::enable_if_t<
                std::is_convertible_v<
                    Y*,
                    element_type*>,
                int> = 0>
        inline explicit BSTSmartPointer(Y* a_rhs) :
            _ptr(a_rhs)
        {
            TryAttach();
        }
 
        // 9a
        inline BSTSmartPointer(const BSTSmartPointer& a_rhs) :
            _ptr(a_rhs._ptr)
        {
            TryAttach();
        }
 
        // 9b
        template <
            class Y,
            std::enable_if_t<
                std::is_convertible_v<
                    Y*,
                    element_type*>,
                int> = 0>
        inline BSTSmartPointer(const BSTSmartPointer<Y>& a_rhs) :
            _ptr(a_rhs._ptr)
        {
            TryAttach();
        }
 
        // 10a
        inline BSTSmartPointer(BSTSmartPointer&& a_rhs) noexcept :
            _ptr(std::move(a_rhs._ptr))
        {
            a_rhs._ptr = nullptr;
        }
 
        // 10b
        template <
            class Y,
            std::enable_if_t<
                std::is_convertible_v<
                    Y*,
                    element_type*>,
                int> = 0>
        inline BSTSmartPointer(BSTSmartPointer<Y>&& a_rhs) noexcept :
            _ptr(std::move(a_rhs._ptr))
        {
            a_rhs._ptr = nullptr;
        }
 
        inline ~BSTSmartPointer()
        {
            TryDetach();
        }
 
        // 1a
        inline BSTSmartPointer& operator=(const BSTSmartPointer& a_rhs)
        {
            if (this != std::addressof(a_rhs)) {
                TryDetach();
                _ptr = a_rhs._ptr;
                TryAttach();
            }
            return *this;
        }
 
        // 1b
        template <
            class Y,
            std::enable_if_t<
                std::is_convertible_v<
                    Y*,
                    element_type*>,
                int> = 0>
        inline BSTSmartPointer& operator=(const BSTSmartPointer<Y>& a_rhs)
        {
            TryDetach();
            _ptr = a_rhs._ptr;
            TryAttach();
            return *this;
        }
 
        // 2a
        inline BSTSmartPointer& operator=(BSTSmartPointer&& a_rhs)
        {
            if (this != std::addressof(a_rhs)) {
                TryDetach();
                _ptr = std::move(a_rhs._ptr);
                a_rhs._ptr = nullptr;
            }
            return *this;
        }
 
        // 2b
        template <
            class Y,
            std::enable_if_t<
                std::is_convertible_v<
                    Y*,
                    element_type*>,
                int> = 0>
        inline BSTSmartPointer& operator=(BSTSmartPointer<Y>&& a_rhs)
        {
            TryDetach();
            _ptr = std::move(a_rhs._ptr);
            a_rhs._ptr = nullptr;
            return *this;
        }
 
        inline void reset()
        {
            TryDetach();
        }
 
        template <
            class Y,
            std::enable_if_t<
                std::is_convertible_v<
                    Y*,
                    element_type*>,
                int> = 0>
        inline void reset(Y* a_ptr)
        {
            if (_ptr != a_ptr) {
                TryDetach();
                _ptr = a_ptr;
                TryAttach();
            }
        }
 
        [[nodiscard]] constexpr element_type* get() const noexcept
        {
            return _ptr;
        }
 
        [[nodiscard]] explicit constexpr operator bool() const noexcept
        {
            return static_cast<bool>(_ptr);
        }
 
        [[nodiscard]] constexpr element_type& operator*() const noexcept
        {
            assert(static_cast<bool>(*this));
            return *_ptr;
        }
 
        [[nodiscard]] constexpr element_type* operator->() const noexcept
        {
            assert(static_cast<bool>(*this));
            return _ptr;
        }
 
    protected:
        template <class, template <class> class>
        friend class BSTSmartPointer;
 
        inline void TryAttach()
        {
            if (_ptr) {
                reference_manager::Acquire(_ptr);
            }
        }
 
        inline void TryDetach()
        {
            if (_ptr) {
                reference_manager::Release(_ptr);
                _ptr = nullptr;
            }
        }
 
        // members
        element_type* _ptr;  // 0
    };
    static_assert(sizeof(BSTSmartPointer<void*>) == 0x8);
 
    template <class T, class... Args>
    [[nodiscard]] inline BSTSmartPointer<T> make_smart(Args&&... a_args)
    {
        return BSTSmartPointer<T>{ new T(std::forward<Args>(a_args)...) };
    }
 
    template <class T1, class T2>
    [[nodiscard]] constexpr bool operator==(const BSTSmartPointer<T1>& a_lhs, const BSTSmartPointer<T2>& a_rhs)
    {
        return a_lhs.get() == a_rhs.get();
    }
 
    template <class T1, class T2>
    [[nodiscard]] constexpr bool operator!=(const BSTSmartPointer<T1>& a_lhs, const BSTSmartPointer<T2>& a_rhs)
    {
        return !(a_lhs == a_rhs);
    }
 
    template <class T>
    [[nodiscard]] constexpr bool operator==(const BSTSmartPointer<T>& a_lhs, std::nullptr_t) noexcept
    {
        return !a_lhs;
    }
 
    template <class T>
    [[nodiscard]] constexpr bool operator==(std::nullptr_t, const BSTSmartPointer<T>& a_rhs) noexcept
    {
        return !a_rhs;
    }
 
    template <class T>
    [[nodiscard]] constexpr bool operator!=(const BSTSmartPointer<T>& a_lhs, std::nullptr_t) noexcept
    {
        return static_cast<bool>(a_lhs);
    }
 
    template <class T>
    [[nodiscard]] constexpr bool operator!=(std::nullptr_t, const BSTSmartPointer<T>& a_rhs) noexcept
    {
        return static_cast<bool>(a_rhs);
    }
 
    template <class T>
    BSTSmartPointer(T*) -> BSTSmartPointer<T, BSTSmartPointerIntrusiveRefCount>;
 
    template <class T>
    using BSTAutoPointer = BSTSmartPointer<T, BSTSmartPointerAutoPtr>;
    static_assert(sizeof(BSTAutoPointer<void*>) == 0x8);
}
 
#define BSSmartPointer(className) \
    class className;              \
    using className##Ptr = RE::BSTSmartPointer<className>;