Re: dynamic_cast is ugly!

Nick Keighley <>
Mon, 17 Mar 2008 04:20:29 -0700 (PDT)
On 16 Mar, 23:42, Juha Nieminen <nos...@thanks.invalid> wrote:

Daniel T. wrote:

Juha, you snip rather generously!

Excellent post!

  All I understood from his post was: If you have a feature which is
common to *all* the objects, put that feature in the base class.

expect that ean't the issue. It was if a feature is common to all su-
of a particular sub-type- then make it a static property. Sounds quite
to me

  Well, duh. Hello? That isn't the issue here at all. (*Of course* I do
that every time I can. You don't have to tell me that.)

  The issue is that some derived classes might have features which do
not belong to the base class at all. (And, in some cases, couldn't even
be added there.)

Read The Code

this is the "excellent" post
the request
should be dealt with much more abstractly -- something more like
"highlight interfaces", using a relatively abstract description of
desired action instead of directly describing its physical

Although I can't say I've seen a use for this specifically in UML,
assume for the moment that it really was something you wanted. In
case, I think stepping through the collection of all the objects and
setting the interfaces to highlighted is only a minor improvement
stepping through them and setting rectangles to yellow.

Instead, if we want to be able to highlight all the interfaces (or
whatever) we'd share the "highlighted" vs. "normal" state (or perhaps
the current color) among all objects of that type:

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


class UML_interface : public UML_object {
        static color_t color;
        static void highlight(bool state=true) {
                static color_t colors[] = {
                        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 {
        UML_class(int x, int y) : x_(x), y_(y) {}

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


color_t UML_interface::color;


Nick Keighley

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