Communicating between in and out contracts

[Leandro Lucarella]

Rainer Deyke, el 17 de octubre a las 14:24 me escribiste:
> Christopher Wright wrote:
> > Rainer Deyke wrote:
> >> It seems that Eiffel had 'old' semantics that I've proposed all along.
> >> Any significant problems with this approach would have been discovered
> >> by the Eiffel community by now.
> > 
> > It requires duplicating the object. If the object is mutable, this
> > requires duplicating it and recursively duplicating everything it
> > references. If the object is immutable, this is free.
> 
> There is no "the object".
> 
>   void f(string fname) out {
>     file_size(fname) >= old(file_size(fname));
>   }

There is an object if you have this:

void f(SomeObjectWithLotsOfReferences obj) out {
  assert(old(obj).some_check());
}

But I don't see why the only option is too recursively copy the entire
object. You can do a shallow copy too. It's a little more error prone
since the programmer need to ensure that all needed "old" references are
kept, but it's realistic. And you have the exact same problem with the
ugly-nasty-oh-please-don't-do-it-like-that associative array of variant
approach too =)

So, if you *really* think that this "old stuff" is needed for contracts,
I prefer the old() approach than the ugly-nasty-...-that associative array
of variant =P

-- 
Leandro Lucarella (AKA luca)                     http://llucax.com.ar/
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