[boost] Re: Re: In-place construction for variant

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2003-10-29 21:00:14

"E. Gladyshev" <egladysh_at_[hidden]> escribió en el mensaje
news:20031030012929.90953.qmail_at_web40803.mail.yahoo.com...
>
> --- David Abrahams <dave_at_[hidden]> wrote:
> [...]
>
> > Can you give a "scientific" definition of what you mean by
> > "scientific?"
>
>
> I am not sure... some links/discussions/papers/books
> that elaborate on how and when object invariants
> can be broken and how to deal with that practically.
>
> I'd be especially interested to see
> how basic guarantees are useful in practical C++
> programming.
> Perhaps some practical usage cases.
> Are there any special considerations
> for breaking invariants and calling other methods
> of the broken object internally?
>
> You can imaging some examples like the following.
> struct type
> {
>   //invariant is x + y = 10
>   int x;
>   int y;
>
>   void f( int n )
>   {
>      x = n;  //* invariant is broken
>      f1();  //* is this allowed?
>      y = 10-n;  //* invariant restored
>   }
>
The way I see it, if f1() is not public, then the above is most likely OK.
If is it public, then it is most likely not OK.
IMO invariants are an outside-view property of the object's state, thus,
during implementation procedures, these might not hold without it
representing a problem.

HTH

Fernando Cacciola
SciSoft