Re: dynamic_cast is ugly!

From:

Juha Nieminen <nospam@thanks.invalid>

Newsgroups:

comp.lang.c++,comp.object

Date:

Mon, 17 Mar 2008 01:40:37 +0200

Message-ID:

<47ddb07d$0$8168$4f793bc4@news.tdc.fi>

Jerry Coffin wrote:

struct UML_object {
    int x_, y_;
    virtual void draw(surface_t &) = 0;
};

class UML_interface : public UML_object {
    static color_t color;
public:
    static void highlight(bool state=true) {
        static color_t colors[] = {
            RGB(0,0,0),
            RGB(255, 0,0)
        };

        color = colors[state];
        // code to force re-draw goes here.
    }

    square(int x, int y) : x_(x), y_(y) {}

    virtual void draw(surface_t &s) {
        // draw "interface" on specified surface
    }
};

class UML_class : public UML_object {
public:
    UML_class(int x, int y) : x_(x), y_(y) {}

    virtual void draw(surface_t &s) {
        // draw "class" on specified surface
    }
};

I don't really understand what you are doing there. It's not even
valid C++. (And public member variables?)

This way we don't need separate containers OR a dynamic_cast to
highlight all your UML_interface objects

  Maybe one of us is missing the point here?

  The problem is not how to implement a feature which is common to all
the objects. The problem is how to implement a feature which is not.

  Of course if a feature is common to all the objects (such as your
highlighting above), you simply make that feature part of the base
class. The problem is that not all features are common to all objects
and cannot be logically placed in the base class.