Andrei Alexandrescu Wrote:
> Walter Bright wrote:
> > Rainer Deyke wrote:
> >> Andrei Alexandrescu wrote:
> >>> Eiffel offers the "old" keyword that refers to the old object in a
> >>> postcondition. But it seems quite wasteful to clone the object just to
> >>> have a contract look at a little portion of the old object.
> >>
> >> You don't need to clone the whole object. You just need to cache the
> >> properties that are used with 'old'.
> >
> > That's a good idea.
>
> Should work, but it has more than a few subtleties. Consider:
>
> class A {
> int fun() { ... }
> int gun(int) { ... }
>
> int foo()
> in {
> }
> out(result) {
> if (old.fun())
> assert(old.gun(5));
> else
> assert(old.fun() + old.gun(6));
> foreach (i; 1 .. old.fun())
> assert(gun(i * i));
> }
> ...
> }
>
> Now please tell what's cached and in what order.
>
>
> Andrei
if fun or gun is impure, then they should not be callable by the contracts.
Because of that, order is irrelevant.
