bitsery/examples/smart_pointers_with_polymorphism.cpp

//
// Created by fraillt on 18.4.26.
//
#include <cassert>
#include <memory>
#include <bitsery/bitsery.h>
#include <bitsery/traits/vector.h>
#include <bitsery/adapter/buffer.h>
#include <bitsery/ext/pointer.h>
#include <bitsery/ext/inheritance.h>
#include <bitsery/ext/std_smart_ptr.h>

//in order to work with polymorphic types, we need to describe few steps:
// 1) describe relationships between base and derived types
// this will allow to know what are possible types reachable from base class
// 2) bind serializer to base class
// this will allow to iterate through all types, and add serialization functions,
// without this step compiler would simply remove functions that are not bound at compile-time even it we use type at runtime.

using bitsery::ext::BaseClass;

using bitsery::ext::PointerObserver;
using bitsery::ext::StdSmartPtr;

//define our data structures
struct Color {
    float r{}, g{}, b{};
    bool operator == (const Color& o) const {
        return std::tie(r, g, b) ==
               std::tie(o.r, o.g, o.b);
    }

};

struct Shape {
    Color clr{};
    virtual ~Shape() = 0;
};

Shape::~Shape() = default;

struct Circle : Shape {
    int32_t radius{};
    bool operator == (const Circle& o) const {
        return std::tie(radius, clr) ==
               std::tie(o.radius, o.clr);
    }

};

struct Rectangle : Shape {
    int32_t width{};
    int32_t height{};
    bool operator == (const Rectangle& o) const {
        return std::tie(width, height, clr) ==
               std::tie(o.width, o.height, o.clr);
    }
};

struct RoundedRectangle : Rectangle {
    int32_t radius{};
    bool operator == (const RoundedRectangle& o) const {
        return std::tie(radius, static_cast<const Rectangle&>(*this)) ==
               std::tie(o.radius, static_cast<const Rectangle&>(o));
    }
};

//define serialization functions
template<typename S>
void serialize(S &s, Color &o) {
    //in real world scenario, it might be possible to serialize this using ValueRange, to map values in smaller space
    //but for the sake of this example keep it simple
    s.value4b(o.r);
    s.value4b(o.g);
    s.value4b(o.b);
}

template<typename S>
void serialize(S &s, Shape &o) {
    s.object(o.clr);
}

template<typename S>
void serialize(S &s, Circle &o) {
    s.ext(o, bitsery::ext::BaseClass<Shape>{});
    s.value4b(o.radius);
}

template<typename S>
void serialize(S &s, Rectangle &o) {
    s.ext(o, bitsery::ext::BaseClass<Shape>{});
    s.value4b(o.width);
    s.value4b(o.height);
}

template<typename S>
void serialize(S &s, RoundedRectangle &o) {
    s.ext(o, bitsery::ext::BaseClass<Rectangle>{});
    s.value4b(o.radius);
}

//define our test structure
struct SomeShapes {
    std::vector<std::shared_ptr<Shape>> sharedList;
    std::unique_ptr<Shape> uniquePtr;
    //weak ptr and refPtr will point to sharedList
    std::weak_ptr<Shape> weakPtr;
    Shape* refPtr;
};

//creates object, and populates some data
SomeShapes createData() {
    SomeShapes data{};
    {
        auto tmp = new RoundedRectangle{};
        tmp->height = 151572;
        tmp->width = 488795;
        tmp->radius = 898;
        tmp->clr.r = 0.5f;
        tmp->clr.g = 1.0f;
        tmp->clr.b = 1.0f;
        data.uniquePtr.reset(tmp);
    }
    {
        auto tmp = new Circle{};
        tmp->radius = 75987;
        tmp->clr.r = 0.5f;
        tmp->clr.g = 0.0f;
        tmp->clr.b = 1.0f;
        data.sharedList.emplace_back(tmp);
    }
    {
        auto tmp = new Rectangle{};
        tmp->height = 15157;
        tmp->width = 48879;
        tmp->clr.r = 1.0f;
        tmp->clr.g = 0.0f;
        tmp->clr.b = 0.0f;
        data.sharedList.emplace_back(tmp);
    }
    data.weakPtr = data.sharedList[0];
    data.refPtr = data.sharedList[1].get();

    return data;
}


template<typename S>
void serialize(S &s, SomeShapes &o) {
    s.ext(o.uniquePtr, StdSmartPtr{});
    // to make things more interesting first serialize weakPtr and refPtr,
    // even though objects that weakPtr and refPtr is serialized later,
    // bitsery will work regardless
    s.ext(o.weakPtr, StdSmartPtr{});
    s.ext(o.refPtr, PointerObserver{});
    s.container(o.sharedList, 100, [](S& s, std::shared_ptr<Shape> &item) {
        s.ext(item, StdSmartPtr{});
    });
}

// STEP 1
// define relationships between base and derived classes

namespace bitsery {
    namespace ext {

        //for each base class define DIRECTLY derived classes
        //e.g. PolymorphicBaseClass<Shape> : PolymorphicDerivedClasses<Circle, Rectangle, RoundedRectangle>
        // is incorrect, because RoundedRectangle does not directly derive from Shape
        template<>
        struct PolymorphicBaseClass<Shape> : PolymorphicDerivedClasses<Circle, Rectangle> {
        };

        template<>
        struct PolymorphicBaseClass<Rectangle> : PolymorphicDerivedClasses<RoundedRectangle> {
        };
    }
}

// convenient type that stores all our types, so that we could easily register and
// also it automatically ensures, that classes is registered in the same order for serialization and deserialization
using MyPolymorphicClassesForRegistering = bitsery::ext::PolymorphicClassesList<Shape>;


//use bitsery namespace for convenience
using namespace bitsery;

//some helper types
using Buffer = std::vector<uint8_t>;
using Writer = OutputBufferAdapter<Buffer>;
using Reader = InputBufferAdapter<Buffer>;

//we need to define few things in order to work with polymorphism
//1) we need pointer linking context to work with pointers
//2) we need polymorphic context to be able to work with polymorphic types
using TContext = std::tuple<ext::PointerLinkingContext, ext::PolymorphicContext<ext::StandardRTTI>>;
//NOTE:
// RTTI can be customizable, if you can't use dynamic_cast and typeid, and have 'custom' solution
using MySerializer = Serializer<Writer, TContext>;
using MyDeserializer = Deserializer<Reader, TContext>;

//checks if deserialized data is equal
void assertSameShapes(const SomeShapes &data, const SomeShapes &res) {
    {
        auto d = dynamic_cast<RoundedRectangle *>(data.uniquePtr.get());
        auto r = dynamic_cast<RoundedRectangle *>(res.uniquePtr.get());
        assert(r != nullptr);
        assert(*d == *r);
    }
    {
        auto d = dynamic_cast<Circle *>(data.sharedList[0].get());
        auto r = dynamic_cast<Circle *>(res.sharedList[0].get());
        assert(r != nullptr);
        assert(*d == *r);
    }
    {
        auto d = dynamic_cast<Rectangle *>(data.sharedList[1].get());
        auto r = dynamic_cast<Rectangle *>(res.sharedList[1].get());
        assert(r != nullptr);
        assert(*d == *r);
    }
    assert(res.weakPtr.lock().get() == res.sharedList[0].get());
    assert(res.refPtr == res.sharedList[1].get());
}

int main() {

    auto data = createData();

    //create buffer to store data
    Buffer buffer{};
    size_t writtenSize{};
    // we will not use quickSerialization/Deserialization functions to show, that we need to register polymorphic classes, explicitly
    {

        //STEP 2
        // before start serialization/deserialization,
        // bind it with base polymorphic types, it will go through all reachable classes that is defined in first step.
        // NOTE: you dont need to add Rectangle to reach for RoundedRectangle
        TContext ctx{};
        std::get<1>(ctx).registerBasesList<MySerializer>(MyPolymorphicClassesForRegistering{});
        //create writer and serialize
        MySerializer ser{ctx, buffer};
        ser.object(data);
        ser.adapter().flush();
        writtenSize = ser.adapter().writtenBytesCount();

        //make sure that pointer linking context is valid
        //this ensures that all non-owning pointers points to data that has been serialized,
        //so we can successfully reconstruct pointers after deserialization
        assert(std::get<0>(ctx).isValid());
    }
    SomeShapes res{};
    {
        TContext ctx{};
        std::get<1>(ctx).registerBasesList<MyDeserializer>(MyPolymorphicClassesForRegistering{});
        //deserialize our data
        MyDeserializer des{ctx, buffer.begin(), writtenSize};
        des.object(res);
        assert(des.adapter().error() == ReaderError::NoError && des.adapter().isCompletedSuccessfully());
        //also check for dangling pointers, after deserialization
        assert(std::get<0>(ctx).isValid());
        // clear shared state from pointer linking context,
        // it is only required if there are any pointers that manage shared state, e.g. std::shared_ptr
        assert(res.weakPtr.use_count() == 2);//one in sharedList and one in pointer linking context
        std::get<0>(ctx).clearSharedState();
        assert(res.weakPtr.use_count() == 1);
    }
    assertSameShapes(data, res);
    return 0;
}