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From: whisd@sersun1.essex.ac.uk (Whiteside S D B)
Newsgroups: comp.lang.c++
Subject: Public vs Private header files in C++
Message-ID: <5243@servax0.essex.ac.uk>
Date: 3 Jun 91 12:23:13 GMT
Article-I.D.: servax0.5243
Sender: news@servax0.essex.ac.uk
Reply-To: whisd@essex.ac.uk (Whiteside S D B)
Organization: University of Essex, Colchester, UK
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I wonder if anyone has any suggestions on this:

Modula-2, for example, provides a separate "public" interface to the user's
of a module. The "definition module" is like a header file - it shows
what functions are available to the user, but it need not show private
functions nor the design of the data structures it uses.

In C++ you have private/public/protected members, but the header file
must contain reference to all these things, regardless of whether the
user needs to see them or not.

This means:
i) security might be compromised: it's possible for the user to "hack" into
the data structures

ii) when implementation-specific features are changed (such as, in a recent
case with me, where I wanted a different sized array in my class) which 
do not change the semantics of the class, the user has to be recompiled as
it has access to the same information as the class itself.

iii) The user is burdened with too much detail when using the header file
as a documentation aid.

Can these be overcome with existing C++ constructs? Or would a change in the
language allowing "incomplete" class declarations for public header files
be needed?

Thanks for any comments.

Simon Whiteside