Arbutils/src/Memory/BorrowedPtr.hpp

#ifndef ARBUTILS_BORROWEDPTR_HPP
#define ARBUTILS_BORROWEDPTR_HPP

#include <memory>
#include "../Assert.hpp"

namespace ArbUt {
    /// A borrowed pointer is used to indicate a pointer that is not owned by an object, but instead borrowed from
    /// another owning object that is assumed to always be kept alive during the entire lifetime of the borrowing
    /// object.
    template <class T> class BorrowedPtr {
    private:
        T* _raw;

    public:
        inline BorrowedPtr<T>() noexcept : _raw(nullptr){};
        inline BorrowedPtr<T>(T* ptr) noexcept : _raw(ptr){};
        inline BorrowedPtr<T>(const BorrowedPtr<T>& other) noexcept : _raw(other._raw){};
        inline BorrowedPtr<T>(const std::unique_ptr<T>& other) noexcept : _raw(other.get()){};

        ~BorrowedPtr() noexcept = default;

        inline BorrowedPtr<T>& operator=(const BorrowedPtr<T>& rhs) noexcept {
            _raw = rhs._raw;
            return *this;
        }

        inline T* operator->() const noexcept {
            AssertNotNull(_raw);
            return _raw;
        }
        inline T operator*() const noexcept {
            AssertNotNull(_raw);
            return *_raw;
        }

        inline T* GetRaw() const noexcept { return _raw; }

        inline bool operator==(const BorrowedPtr& rhs) const noexcept { return _raw == rhs._raw; }
        inline bool operator!=(const BorrowedPtr& rhs) const noexcept { return _raw != rhs._raw; }

        [[nodiscard]] inline constexpr bool IsNull() const noexcept { return _raw == nullptr; }

        inline BorrowedPtr<const T> Const() const noexcept { return BorrowedPtr<const T>(_raw); }

        template <class TCast> inline BorrowedPtr<TCast> As() const {
            auto cast = dynamic_cast<TCast*>(_raw);
            return BorrowedPtr<TCast>(cast);
        }

        template <class TCast> inline bool TryAs(BorrowedPtr<TCast>& out) const noexcept {
            auto cast = dynamic_cast<TCast*>(_raw);
            if (cast == nullptr)
                return false;
            out = BorrowedPtr<TCast>(cast);
            return true;
        }

        template <class TCast> inline BorrowedPtr<TCast> ForceAs() const noexcept {
            auto cast = reinterpret_cast<TCast*>(_raw);
            return BorrowedPtr<TCast>(cast);
        }
    };
}

namespace std {
    template <class T> struct hash<ArbUt::BorrowedPtr<T>> {
        std::size_t operator()(const ArbUt::BorrowedPtr<T>& k) const { return (size_t)k.GetRaw(); }
    };
}

#endif // ARBUTILS_BORROWEDPTR_HPP