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From: kempf@hplabsz.HPL.HP.COM (Jim Kempf)
Newsgroups: comp.lang.c++
Subject: Paramaterized Types and Inheritance (was: C++ libraries)
Message-ID: <817@hplabsz.HPL.HP.COM>
Date: Tue, 29-Sep-87 11:13:50 EDT
Article-I.D.: hplabsz.817
Posted: Tue Sep 29 11:13:50 1987
Date-Received: Thu, 1-Oct-87 04:02:55 EDT
References: <1096@g.gp.cs.cmu.edu>
Organization: Hewlett-Packard Laboratories
Lines: 33
Summary: Be careful!

In article <1096@g.gp.cs.cmu.edu>, dld@g.gp.cs.cmu.edu (David Detlefs) writes:
> 
>   How do inheritance and parameterized classes interact?  I think that

I would be very careful indeed about introducing both multiple inheritance
and parameterized types into a language without careful thought about
how the two interact. C++ is already a fairly rich language, and addition
of other constructs may push it over the brink. Those who complain about
excessive featurism in Ada and see C++ as relief should be concerned.

I am even a little uneasy about introducting multiple inheritance into
a language like C++ which depends on traditional linker/library technology
for software reuse. The semantics of multiple inheritance are difficult
even in a language like Common Lisp, where a more flexible linking discipline
gives the language developer more control, and a richer runtime environment
allows more information about libraries to be made available. The issue
is not just one of implementation, but also whether the semantics match
well with the programmer's model of how to do things, and whether the
programming environment can support the additional load. I realize that
competition from Eiffel (which has parameterized types and multiple
inheritance) is tight, but Eiffel provides somewhat more in the way
of software tools for dealing with the extra complexity, and, thought
I've never used Eiffel, I'm not convinced that these tools would make
much of a difference anyway, since the runtime environment in Eiffel is
also fairly impoverished with respect to languages like Smalltalk and
Lisp.

Somebody ought to look into a formal semantics, whether algebraic,
denotational, or abstract is irrelevent, of C++. With that in hand,
the effect of an addition like parameterized classes can be better
assessed.

		Jim Kempf	kempf@hplabs.hp.com