Potential idea for conditional data in a network packet

netcode Blah.cpp

class Blah {
    enum {
        net_X_pos = (1 << 0),
        net_Y_pos = (1 << 1),
        net_OtherVar = (1 << 2),
        net_AnotherVar = (1 << 3),
        ...
    };

private:
    int dirty_flags_;
    float x_pos_;
    float y_pos_;
    int othervar_;
    char anothervar_;

public:
    void setXPos(float x) {
        this->x_pos_ = x;
        this->dirty_flags_ |= net_X_pos;
        /* Setter methods need to update the dirty_flags_ */
    }

    void ReadNetworkPacket(Stream* s) {
        int flags = S->readInt();

        if (flags & net_X_pos) {
            this->x_pos_ = S->readFloat();
        }
        if (flags & net_Y_pos) {
            this->y_pos_ = S->readFloat();
        }
        if (flags & net_OtherVar) {
            this->othervar_ = S->readInt();
        }
        if (flags & net_AnotherVar) {
            this->anothervar_ = S->readChar();
        }
    }

    /* When you write the fields to a stream, set dirty_flags_ back to 0 */
};