Hi out there,

I am currently fighting with my C++ compiler to teach it redefinition of
function arguments. However, it refuses to do as I like it to, and I was
wondering if anyone could help me out of this...

I have a class called `Model' and an associated class `Interface'. These two
work together in the following way (private and protected clauses left out
for brevity):

class Interface
{
  Interface();   // initializes interface stuff
  ~Interface();   // releases memory etc.
  virtual interact();
};

class Model
{
  Model();
  ~Model();
  virtual loop(Interface *);
};

The idea about this is to get an abstract view of applications; every
application enters a main processing `loop', out of which it returns if
finished. Every user interface is initialized and then we can handle the
interaction with the user in the central processing loop `interact'.

Now, if I want to model an application with the property of having one flag
that is in some unknown way toggled by the user (say, a button in a window),
I may define:

class FlagModel: public Model
{
  virtual loop(Interface *);
};

class ButtonInterface: public Interface
{
  int flagIsOn;
  ButtonInterface();
  ~ButtonInterface();
  virtual interact();
};

This, however, is no clean solution to my problem, as the `FlagModel' assumes
to be coupled with an `Interface' with an additional property, i.e.
`flagIsOn'. And that can not be asserted, as the argument to `loop' is an
`Interface', but not a `ButtonInterface'. This is what I need argument
refinement for. In my mind, I could simply state:

class FlagModel: public Model
{
  virtual loop(ButtonInterface *);
};

But here the trouble starts: my compiler (gcc to be exact) expects
`virtual loop(Interface *)' to be defined and implemented in `FlagModel', but
I don't want to allow for this. If I leave out definition and implementation
of this function, I get an `unknown symbol' error at link time.

Thus, to come to an end, my question is: Is this a feature of standard C++, of
gcc in particular or not? And if it is, is there a workaround?

Any pointers or direct e-mail greatly appreciated.

 HW

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