Re: [boost] Proposal: statefull objects

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-07-20 10:51:04

From: "Fernando Cacciola" <fcacciola_at_[hidden]>
> From: Peter Dimov <pdimov_at_[hidden]>
> > From: "Fernando Cacciola" <fcacciola_at_[hidden]>
> > > How should we deal with the case of x,y being outside the image?
> >
> > A function should not try to do too many things.
> >
> > bool is_inside(int x, int y) const;
> > color_type get_pixel(int x, int y) const;
> >
> My point is not about returning pixels from an image. It is just an
example.
> I'm sure you can come out with an example that suits you. (A function that
> might not return a value in a situation were that is not an exception).

I didn't mean to imply that stateful<T> is not useful. I just think that
"case A" is not a good demonstration of its usefulness, that's all.

> Or simply take the case of set/map insert().

Actually this is a bit different. The associative insert() always returns a
valid iterator, regardless of whether the 'bool' part is true. You'll have
to decide whether your class is a discriminated union (you can't extract a
value from it when it's empty(), operator* leads to undefined behaviour) or
a (T, bool) pair.

> You may think that I am solving my problems the wrong way, just like you
did
> with respect to the image example,

No, not at all, sorry for giving the wrong impression.

--
Peter Dimov
Multi Media Ltd.