Re: Generic Package

[Georg Bauhaus <rm.tsoh+bauhaus@maps.futureapps.de>]

On Wed, 2007-05-02 at 15:12 +0200, Dmitry A. Kazakov wrote:
> On Wed, 02 May 2007 13:48:26 +0200, Georg Bauhaus wrote:
> 
> > On Wed, 2007-05-02 at 12:29 +0200, Dmitry A. Kazakov wrote:
> > 
> >>> Memory is not abstract, addresses aren't abstract,
> >> 
> >> In what sense? 
> > 
> > When you write a Set implementation for a PC, you can specifying
> > addresses and refer to addresses in a consistent way.
> 
> But I am not required to do so.

(I'll listen to Randy who said: "In any case, this is an Ada forum,
and abstractions that you cannot describe in Ada are simply not
relevant", and be brief, for one more time only.)

>  Now, let you have a container holding 1, 2, 3, can you
> point me the address of 2 there?

Yes. It is between 1 and 3, the docs say. Whether it actually is a
computer address between 1'Address and 3'Address is a matter of
implementation, but I can base arguments on 2 being between 1 and 3.
But anyway, I don't have to at all because my Iterator is fine with
any permutation of {1,2,3}. Let the implementation magic pick
some first element.


> BTW 2, it is sort of surprising to have such a discussion in c.l.a., for
> Ada was one of the first languages introducing a clear distinction between
> interface and implementation.

Ada has interfaces, implementations, and a publicly available LRM which,
in part, informs its readers about what to expect from behind some
interfaces, in abstract terms I would say :-)


> >> or
> >> 
> >> 2. The program is incorrect,

Precondition on local Count_Var together with Add_One before
calling Foreach...
I had given an argument about the correctness of the program WRT
some model of how Foreach works. When a container doesn't provide
an interface for expressing all preconditions, OK. Then the
precondition refers to different things and it is up to the container
to maintain invariants, no?



 
> >> Ordering is determined by sole existence of the
> >> librarian who can give you a [first] book and continue to do so.
> > 
> > That is, ordering is an outcome of the librarians operation,
> > not of the books.
> 
> Come on, all orderings are ordered but some orderings are more ordered than
> others? (:-)) _WHAT_ is the difference?  Let you asked somebody to bring
> you books in their "proper" order. How can you determine if he does not
> cheat?

I don't check an order that I don't know, can't know, and don't care
about.