Re: on OO differnces between Ada95 and C++

[Simon Johnston <skj@ACM.ORG>]

> ...YET ANOTHER RELIGIOUS WAR...

Lets hope not.

> Pete Becker wrote:
>
> > >#define private public // *** BERK! ***
> > >#include "...h"        // second definition for the same class
> > >#undef private
> >
> > This is not true. A program that attempts to do this violates the one
> > definition rule, so it is not a legal C++ program.
>
> Pete,
>
> What is this "one definition rule"? Could you point me to the
> appropriate C++ Draft Standard location?

  [snip]

> The whole program contains two definitions for the same classes Shape
> and Rectangle: for each, one definition with attributes private and
> another definition with everything public.

The whole program does, the point is that no one single compilation stream
must include more than one definition for a given entity.

> It seems that in C++, every encapsulation can be legally broken,
> essentially because of _independent_ compilation that allows
> redefinitions of the same class.
>
> Ada compilation model is different: it's _separate_ compilation.
> Impossible in Ada to have a redefinition in the same program: it's
> detected at compile-time. If something is checked in C++, it's deferred
> to link-time (for example a redefinition of the same class that will
> clash because the two constructors will have the same name).
>
>
> Read also "The design and evolution of C++" by Bjarne Stroustrup,
> chapter 17 "Namespaces", section 3 "Ideals for a solution": Ada has a
> more complete solution than C++.
>
> The basic property of OO languages is encapsulation. According to this
> criteria, C++ fails.
>
> Non mais enfin, quoi !
>
>
>   Jerome.
>
>

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