Re: Ada vs Eiffel - Ada programmer approach

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

On Jun 4, 9:30 am, Hibou57 (Yannick Duchêne)
<yannick_duch...@yahoo.fr> wrote:
> On 26 mai, 15:37, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
>
> > [...] Ada's pragma Assert provides what I
> > need in these (rare) cases  because I can put such pragmas in the
> > middle of a subprogram, for example.
>
> > --
> > Ludovic Brenta.
>
> This is not the same as Eiffel assertions. Eiffel's assertions are
> aware of the invokation contexte. Let say you have a class C and a
> method M and the class C has an invariant I. Then, if a client invoks
> M, the invariant will be checked before M returns. That's Ok, this is
> the same as with "in code assertions". But if M is invoked by anoher
> method of the class, i.e. as an implementation method (this is very
> common to use a public method for internal purpose), you will have
> this : the client of C invok a method M2 which in turn will invok M
> (the client may or may not know about it). In this context, the class
> invariant will obviously be checked before returning from M2, but *it
> will not be check before return from M*.
>
> That is beceause M is allowed to left the class invariant in an
> illegal state, as it may be the sole responsability of M2.
>
> So, Eiffel's assertions are not the same as "in code assertions".
> Eiffel's assertions are well formalized.

I think my point was precisely that Ada assertions were different from
Eiffel's. I like the fact that, in Ada, I can place assertions in the
middle of a complex subprogram; this is not possible Eiffel, as you
aptly described. I agree that Eiffel's assertions are well-defined but
my argument is that they are less useful and more diffucult to use in
practice than the beauty of the design suggests.

--
Ludovic Brenta.