C++: Polymorphism

Question

I want to start by showing some code and explain my problem later.

Base class:

class swcObject :
    public swcRectangle
{
public:
    bool visible;
};

Sub-base class[optional, abstract]:

class swcText
{
public:
    std::string text;
protected:
    virtual void attachedToParent() = 0;
};

Derived classes:

class swcLabel :
    public swcObject,
    public swcText
{
public:
    int text_align;
private:
    void attachedToParent();
};

...

class swcComboBox :
    virtual protected swcObject
{
public:
    void setPosition(int x, int y);
private:
     swcLabel label;
};

Now I have this class w/c has a member object of type std::vector<swcObject>.

class swcWindow :
    private swcObject
{
public:
    void addObject(const swcObject &object);
private:
    std::vector<swcObject> objects;
};

I came into this few problems w/c I haven't encountered before and Google seems don't have a relevant problem like mine.

My specific problems are:

---

Relevant code:

swcWindow window;
swcComboBox cbox;

window.addObject(cbox);

Error:

'swcObject' is an inaccessible base of 'swcComboBox'

Desire:

I do not want to access swcComboBox::swcObject members on public scope like this cbox.x = 0;, but instead cbox.setPosition(0, 0); because there will be always an adjusting of some member elements whenever the swcComboBox had changed its location.

---

Relevant code:

swcWindow window;
swcLabel label;

window.addObject(label);

Error:

In this case, label have a base classes of swcText and swcObject. After adding the label to one of member of window.objects (is of type std::vector), swcText properties are gone, like the text property.

Desire:

I want to create a temporary objects and initialize its property in a init() method outside of those classes and copy it using swcWindow::addObject(). Is this possible without a cast? I think this one would do but its awful(?), and I didn't try it yet if this is working:

void addObject(const swcObject &object, SWC_TYPES type)
{
    switch (type)
    {
    case LABEL:
        //do casting?
    ...
    }

}

Please recommend any other way how can I achieve those kind of implementation with the same functionalities.

Answer 1

vector store elements by value, as if you passed your ComboBox to a procedure which takes a swcObject by value, not by reference. This leads to cut of object to its base class, which is prohibited if you use protected inheritance.

You shouldn't store polymorphic objects in vector, just as you shouldn't pass them by value. You can try storing references or (smart) pointers in vector - that should solve your problems.