🚀 go-pugleaf

The class_ID is meant to NOT be virtual...this way it can be used to
register the stream-constructor static routines with URegistrar allowing
easy construction using Constructor.  I suppose a static GetClassID() 
routine would be ok, but there's no real difference there.  If you
want to do a 

myPane->GetClassID()

kind of call, you should probably use RTTI (as far as I've been told) to
determine what kind of object your myPane is.  As far as I know, there's
no other way, other than modifying the PP code itself.

-David

richard@moriarty.com (Richard Jason Lyders) wrote:
>HELP! Suggestions are MOST WELCOME!
>
>Why would someone use an enum for a class_ID in a class library? Why not
>simply provide a GetClassID() function for each class? That would be so
>much simpler and so much more useful!
>
>I don't seem to be able to use the enum class_ID  to find out what class
>an object is because class_ID isn't "virtual" like a function. If you have
>an object of a class that is derived from a base class, and you are
>referencing that object using the base pointer, then class_ID does not
>tell you the class of the object, it tells you the class of the pointer.
>What god is this? I know what class the pointer is because I cast it
>myself! Duh?
>
>This means that I don't seem to be able to create a routine that uses a
>base class as a pointer to any of that base class's derived classes. . .
>because in that routine I need to know exactly what the class_id is of the
>REAL object rather than the class_ID of the base object (which is pretty
>darn obvious because it never changes).
>
>I did not expect to run into this problem. Is this a limitation? an error
>on my part? Is there another way to find out the actual class of an object
>without using a class_ID enum that really will give me the correct
>class_ID?
>
>So , by using an enum . . .whatever you type cast a pointer as. . . that's
>the class ID that you get. . . so it isn't any better than a compiler
>#define as far as I am trying to use it.
>
>If you check out my code example below. . .you will see my confusion as to
>why a class_ID enum would be used . . . and I hope ther is another way of
>finding out an object's actual class ID.
>
>PS: and no, it is not possible to give each class a GetClassID routine
>because I am having this problem with the Metrowerks PowerPlant class
>library and I don't think it is very acceptible to  just go around
>changing the inner workings of a class library.
>
>class LPane {
>   public:
>      enum { class_ID = 'pane' };
>      LPane() {};
>      ~LPane() {}; 
>};
>
>class LView : public LPane {
>   public:
>      enum { class_ID = 'view' };
>      LView() {};
>      ~LView() {};
>};
>
>void main (void) {
> LPane aPane;
> LView aView;
> LPane * aPanePtr = &aPane;
> LView * aViewPtr =  &aView;
> LPane * aPanePtr2 = (LPane*)aViewPtr;
> 
> long aPaneClassID = aPanePtr->class_ID;    // = 'pane' (obviously) 
> long aViewClassID = aViewPtr->class_ID;    // = 'view' (obviously)
> long aWhichClassID = aPanePtr2->class_ID;  // = 'pane' ********* why?
>**********
>}
>
>/*                                   
>                                     ?
> ___  o     _             _         /
>| o \ _ ___| |_ ___ _ _ _| |    /"""\
>|   /| | __)   | o | '_| o |    |~'~|       
>|_|_\|_\___)_|_|_|_|_| \___|    \ - /     
>.---------------------------------^----. 
>| Richard Jason Lyders  Houston, Texas |
>|         richard@moriarty.com         |
>'-----------------------------OOo----oOO
>                                |=[]=|       
>                                /_/\_\            
>                               oOO  OOo
>
>*/
>
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