Embedding de-(serialization) into Q_GADGET about qtjsonserializer HOT 2 CLOSED

I see. So what you basically need is a "serialize into" method you could call, something like this (from the ctor):

QJsonSerializer s;
s.serializeInto<JsonSerializable>(this, json);

Currently, there is no such feature. But there is one problem with your Idea in general. How do you want to handle subclassing? E.g. if you have a class MyGadget that extends JsonSerializable - how do you want to "tell" the JsonSerializable that it needs to deserialize to that type - within a constructor of a base class, it is impossible to know what concrete class is calling it (See https://stackoverflow.com/questions/962132/calling-virtual-functions-inside-constructors for more details)!

So even if that method did exist, you would not be able to deserialize anything with it in the constructor. Also, gadgets do not support polymorphing, so even if the json you deserialize contains information about the concrete class, it cannot be processed by the serializer. You will also have a similar problem when serializing in the tojson method, as the base class somehow needs to now the concrete gadget type! (Please note that this limitation only applies to gadgets - with objects, this would not be a problem at all!)

Instead of having a constructor that takes JSON, I would recommend you to create a static construction method instead. This would solve all of your problems in a simple and elegant way. The following is my idea of implementing a self-serializing class:

class JsonSerializable 
{
    Q_GADGET

public:
    template <typename T>
    static T fromJson(const QByteArray &json) {
        static_assert(std::is_base_of<JsonSerializable, T>::value, "T must extend JsonSerializable");
        QJsonSerializer s;
        return s.deserializeFrom<T>(json);
    }

    QByteArray toJson() const {
        QJsonSerializer s;
        return s.serializeTo(toVariant());
    }
 
protected:
    virtual QVariant toVariant() const = 0;
};

// in every subclass, implement the toVariant method as:

QVariant MyGadget::toVariant() const {
    return QVariant::fromValue(this);
}

I know that it is kind of ugly to have the toVariant method here, but sadly, there is no other way, as once again, gadgets are very limited when it comes to dynamic typing (The reason is that gadgets, unlike objects, do not have a dynamic meta object, only a static one). If you want to avoid this, the only possible way is to use QObject based classes instead.

from qtjsonserializer.

Ok, thank you, I understood your idea.

from qtjsonserializer.