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Newsgroups: comp.lang.ada
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From: jgg@evb.com (John Goodsen)
Subject: Re: Encapsulation in Ada vs. C++ (Was Re: Ichibah [sic] ...)
Message-ID: <1993Mar16.223708.11893@evb.com>
Organization: EVB Software Engineering, Inc.
Date: Tue, 16 Mar 1993 22:37:08 GMT
Date: 1993-03-16T22:37:08+00:00
List-Id: <comp.lang.ada>

magnus@lglsun.epfl.ch (Magnus Kempe) writes:
>
>If your class Foo grants "friendship" to a function/class Bar, _anyone_
>can write such a function/class and, having granted itself "friendliness",
>will have access to the internals of Foo.
>
Oh my!  And shame, shame, shame on you for even thinking imitating
my "BAR".  This argument is remeniscent of the facist arguments which
have the common theme of "you might use it wrong, therefore I want
to keep you from using it at all".  BTW, you won't get too far in
the link stage with both "BAR"s in the system (multiply defined identifiers
and such..)

>
>To repeat: contrary to Ada, C++ does not provide a safe means to create
>subprograms acting on parameters of two or more types (classes).  In
>C++, either you write an unsafe class because the language lacks the
>concept of a module, or you twist around with .h files and say good-bye
>to limited, separate recompilations.
>

"UNSAFE CLASS" ???
Huh?  Come now!  "friendship" is not necessarily unsafe.  Only if you use
it wrong.  True, Ada packaging and "classtypes" (I refuse to use
tagged type syntax anymore ;-) overcome this *perceived* defect
in C++, but to *twist* the truth in suggesting that you lose separate
recompilations is not responsible.  In fact to the contrary, the *friend*
concept allows for separate recompilation of these related classes
and functions.  Ada packages *REQUIRE* recompilation of all related 
"classtypes" (there it is again, isn't it a pretty syntax ;-), since they're
in the same package.  


-- 
John Goodsen
Software Process & Environments
EVB Software Engineering
jgg@evb.com