polymorphism and smart pointers

examples/smart_pointers_with_polymorphism.cpp

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+//
+// 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, 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](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> {
+        };
+    }
+}
+
+//use bitsery namespace for convenience
+using namespace bitsery;
+
+//some helper types
+using Buffer = std::vector<uint8_t>;
+using OutputAdapter = OutputBufferAdapter<Buffer>;
+using InputAdapter = 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 = BasicSerializer<AdapterWriter<OutputAdapter, DefaultConfig>, TContext>;
+using MyDeserializer = BasicDeserializer<AdapterReader<InputAdapter, DefaultConfig>, 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{};
+    {
+        TContext ctx{};
+        MySerializer ser{OutputAdapter{buffer}, &ctx};
+        //STEP 2
+        //bind serializer with base polymorphic types, it will go through all reachable classes that is defined in first step.
+        //so you dont need to add Rectangle to reach for RoundedRectangle
+        std::get<1>(ctx).registerBasesList(ser, ext::PolymorphicClassesList<Shape>{});
+        //serialize our data
+        ser.object(data);
+        auto &w = AdapterAccess::getWriter(ser);
+        w.flush();
+        writtenSize = w.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{};
+        MyDeserializer des{InputAdapter{buffer.begin(), writtenSize}, &ctx};
+        //same as in serialization
+        std::get<1>(ctx).registerBasesList(des, ext::PolymorphicClassesList<Shape>{});
+        //serialize our data
+        des.object(res);
+        auto &r = AdapterAccess::getReader(des);
+        //check if everything went find
+        assert(r.error() == ReaderError::NoError && r.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;
+}