bitsery/include/bitsery/ext/utils/polymorphism_utils.h

//MIT License
//
//Copyright (c) 2018 Mindaugas Vinkelis
//
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#ifndef BITSERY_EXT_POLYMORPHISM_UTILS_H
#define BITSERY_EXT_POLYMORPHISM_UTILS_H

#include <unordered_map>
#include <memory>
#include "memory_allocator.h"
#include "../../details/adapter_common.h"
#include "../../details/serialization_common.h"

namespace bitsery {

    namespace ext {

        //helper type, that contains list of types
        template<typename ...>
        struct PolymorphicClassesList {
        };

        //specialize for your base class by deriving from PolymorphicDerivedClasses with list of derivatives that DIRECTLY inherits from your base class.
//e.g.
// template <> PolymorphicBaseClass<Animal>: PolymorphicDerivedClasses<Dog, Cat>{};
// template <> PolymorphicBaseClass<Dog>: PolymorphicDerivedClasses<Bulldog, GoldenRetriever> {};
// IMPORTANT !!!
// although you can add all derivates to same base like this:
// template <> PolymorphicBaseClass<Animal>:PolymorphicDerivedClasses<Dog, Cat, Bulldog, GoldenRetriever>{};
// it will not work when you try to serialize Dog*, because it will not find Bulldog and GoldenRetriever
        template<typename TBase>
        struct PolymorphicBaseClass {
            using Childs = PolymorphicClassesList<>;
        };

//derive from this class when specifying childs for your base class, atleast one child must exists, hence T1
//e.g.
// template <> PolymorphicBaseClass<Animal>: PolymorphicDerivedClasses<Dog, Cat>{};
        template<typename T1, typename ... Tn>
        struct PolymorphicDerivedClasses {
            using Childs = PolymorphicClassesList<T1, Tn...>;
        };

        class PolymorphicHandlerBase {
        public:
            virtual void* create(const pointer_utils::PolymorphicAllocatorWithTypeId& alloc) const = 0;

            virtual void destroy(const pointer_utils::PolymorphicAllocatorWithTypeId& alloc, void* ptr) const = 0;

            virtual void process(void* ser, void* obj) const = 0;

            virtual ~PolymorphicHandlerBase() = default;
        };

        template<typename RTTI, typename TSerializer, typename TBase, typename TDerived>
        class PolymorphicHandler : public PolymorphicHandlerBase {
        public:

            void* create(const pointer_utils::PolymorphicAllocatorWithTypeId& alloc) const final {
                return toBase(alloc.newObject<TDerived>(RTTI::template get<TDerived>()));
            }

            void destroy(const pointer_utils::PolymorphicAllocatorWithTypeId& alloc, void* ptr) const final {
                alloc.deleteObject<TDerived>(fromBase(ptr), RTTI::template get<TDerived>());
            }

            void process(void* ser, void* obj) const final {
                static_cast<TSerializer*>(ser)->object(*fromBase(obj));
            }

        private:

            TDerived* fromBase(void* obj) const {
                return RTTI::template cast<TBase, TDerived>(static_cast<TBase*>(obj));
            }

            TBase* toBase(void* obj) const {
                return RTTI::template cast<TDerived, TBase>(static_cast<TDerived*>(obj));
            }

        };

        template<typename RTTI>
        class PolymorphicContext {
        private:

            struct BaseToDerivedKey {

                std::size_t baseHash;
                std::size_t derivedHash;

                bool operator==(const BaseToDerivedKey& other) const {
                    return baseHash == other.baseHash && derivedHash == other.derivedHash;
                }
            };

            struct BaseToDerivedKeyHashier {
                size_t operator()(const BaseToDerivedKey& key) const {
                    return (key.baseHash + (key.baseHash << 6) + (key.derivedHash >> 2)) ^ key.derivedHash;
                }
            };

            template<typename TSerializer, template<typename> class THierarchy, typename TBase, typename TDerived>
            void add() {
                addToMap<TSerializer, TBase, TDerived>(std::is_abstract<TDerived>{});
                addChilds<TSerializer, THierarchy, TBase, TDerived>(typename THierarchy<TDerived>::Childs{});
            }

            template<typename TSerializer, template<typename> class THierarchy, typename TBase, typename TDerived, typename T1, typename ... Tn>
            void addChilds(PolymorphicClassesList<T1, Tn...>) {
                static_assert(std::is_base_of<TDerived, T1>::value,
                              "PolymorphicBaseClass<TBase> must derive a list of derived classes from TBase.");
                add<TSerializer, THierarchy, TBase, T1>();
                addChilds<TSerializer, THierarchy, TBase, TDerived>(PolymorphicClassesList<Tn...>{});
                //iterate through derived class hierarchy as well
                add<TSerializer, THierarchy, T1, T1>();
            }

            template<typename TSerializer, template<typename> class THierarchy, typename TBase, typename TDerived>
            void addChilds(PolymorphicClassesList<>) {
            }

            template<typename TSerializer, typename TBase, typename TDerived>
            void addToMap(std::false_type) {
                BaseToDerivedKey key{RTTI::template get<TBase>(), RTTI::template get<TDerived>()};
                if (_baseToDerivedMap
                    .emplace(key, std::make_shared<PolymorphicHandler<RTTI, TSerializer, TBase, TDerived>>())
                    .second)
                    _baseToDerivedArray[key.baseHash].push_back(key.derivedHash);
            }

            template<typename TSerializer, typename TBase, typename TDerived>
            void addToMap(std::true_type) {
                //cannot add abstract class
            }

            std::unordered_map<BaseToDerivedKey, std::shared_ptr<PolymorphicHandlerBase>, BaseToDerivedKeyHashier> _baseToDerivedMap{};
            // this will allow convert from platform specific type information, to platform independent base->derived index
            // this only works if all polymorphic relationships (PolymorphicBaseClass<TBase> -> PolymorphicDerivedClasses<TDerived...>)
            // is equal between platforms.
            std::unordered_map<size_t, std::vector<size_t>> _baseToDerivedArray{};

        public:

            void clear() {
                _baseToDerivedMap.clear();
                _baseToDerivedArray.clear();
            }

            // THierarchy is the name of class, that defines hierarchy
            // PolymorphicBaseClass is defined as default parameter, so that at instantiation time
            // it will get unique symbol in translation unit for PolymorphicBaseClass (which is defined in anonymous namespace)
            // https://github.com/fraillt/bitsery/issues/9
            template<typename TSerializer, template<typename> class THierarchy = PolymorphicBaseClass, typename T1, typename ...Tn>
            void registerBasesList(PolymorphicClassesList<T1, Tn...>) {
                add<TSerializer, THierarchy, T1, T1>();
                registerBasesList<TSerializer, THierarchy>(PolymorphicClassesList<Tn...>{});
            }

            template<typename TSerializer, template<typename> class THierarchy>
            void registerBasesList(PolymorphicClassesList<>) {
            }

            // optional method, in case you want to construct base class hierarchy your self
            template<typename TSerializer, typename TBase, typename TDerived>
            void registerSingleBaseBranch() {
                static_assert(std::is_base_of<TBase, TDerived>::value, "TDerived must be derived from TBase");
                static_assert(!std::is_abstract<TDerived>::value, "TDerived cannot be abstract");
                addToMap<TSerializer, TBase, TDerived>(std::false_type{});
            }


            template<typename Serializer, typename Writer, typename TBase>
            void serialize(Serializer& ser, Writer& writer, TBase& obj) const {
                //get derived key
                BaseToDerivedKey key{RTTI::template get<TBase>(), RTTI::template get<TBase>(obj)};
                auto it = _baseToDerivedMap.find(key);
                assert(it != _baseToDerivedMap.end());

                //convert derived hash to derived index, to make it work in cross-platform environment
                auto& vec = _baseToDerivedArray.find(key.baseHash)->second;
                auto derivedIndex = static_cast<size_t>(std::distance(vec.begin(), std::find(vec.begin(), vec.end(),
                                                                                             key.derivedHash)));
                details::writeSize(writer, derivedIndex);

                //serialize
                it->second->process(&ser, &obj);
            }

            template<typename Deserializer, typename Reader, typename TBase, typename TCreateFnc, typename TDestroyFnc>
            void deserialize(Deserializer& des, Reader& reader, TBase* obj,
                             TCreateFnc createFnc, TDestroyFnc destroyFnc) const {
                size_t derivedIndex{};
                details::readSize(reader, derivedIndex, 0, std::false_type{});

                auto baseToDerivedVecIt = _baseToDerivedArray.find(RTTI::template get<TBase>());
                //base class is known at compile time, so we can assert on this one
                assert(baseToDerivedVecIt != _baseToDerivedArray.end());

                if (baseToDerivedVecIt->second.size() > derivedIndex) {
                    //convert derived index to derived hash, to make it work in cross-platform environment
                    auto derivedHash = baseToDerivedVecIt->second[derivedIndex];
                    auto& handler = _baseToDerivedMap.find(
                        BaseToDerivedKey{RTTI::template get<TBase>(), derivedHash})->second;
                    //if object is null or different type, create new and assign it
                    if (obj == nullptr || RTTI::template get<TBase>(*obj) != derivedHash) {
                        if (obj) {
                            destroyFnc(getPolymorphicHandler(*obj));
                        }
                        obj = createFnc(handler);
                    }
                    handler->process(&des, obj);
                } else
                    reader.error(ReaderError::InvalidPointer);
            }

            template<typename TBase>
            const std::shared_ptr<PolymorphicHandlerBase>& getPolymorphicHandler(TBase& obj) const {
                auto deleteHandlerIt = _baseToDerivedMap.find(
                    BaseToDerivedKey{RTTI::template get<TBase>(), RTTI::template get<TBase>(obj)});
                assert(deleteHandlerIt != _baseToDerivedMap.end());
                return deleteHandlerIt->second;
            }


        };

    }

}

#endif //BITSERY_EXT_POLYMORPHISM_UTILS_H