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From: johnson@p.cs.uiuc.edu
Newsgroups: comp.lang.c++
Subject: Re: Eiffel vs. C++ (vs Smalltalk)
Message-ID: <77300030@p.cs.uiuc.edu>
Date: 10 Jun 89 15:25:00 GMT
References: <5316@tekgvs.LABS.TEK.COM>
Lines: 46
Nf-ID: #R:tekgvs.LABS.TEK.COM:5316:p.cs.uiuc.edu:77300030:000:2432
Nf-From: p.cs.uiuc.edu!johnson    Jun 10 10:25:00 1989


Snorri Agnarsoon (snorri@rhi.hi.is) made some comments about my comments
about assertions.  Though he may not realize it, we agree.

Then, in response to my comment on garbage collection, he says

>In my opinion garbage collection is the single most useful feature
>of a programming language.  Without garbage collection polymorphism
>is severely handicapped and programmers tend to shy away from clean
>designs because of the restrictions imposed by the lack of garbage
>collection.

I am a Smalltalk and a C++ programmer.  Smalltalk is a lot more fun
to use, and I can build systems much faster with it.  Garbage collection
is a major reason, though probably
>In my opinion garbage collection is the single most useful feature
>of Prolog, LISP, SmallTalk, Eiffel, CLU, etc., etc.
is an overstatement.  However, my remark was specifically directed
to real-time programming.  Garbage collection does not get along
very well with real-time programming.  The Smalltalk garbage
collectors are pretty good, usually only taking a fraction of a
second to collect garbage.  However, if this happened in a middle
of an interrupt then even 1/4 a second is too long.

I want every language I use to handle memory allocation and deallocation
automatically.  C++ constructors and destructors are nice, but are still
too much work, and the examples that Snorri gave show that sometimes
they are not sufficient.  However, designing a language so that it
provides complete memory management and still permits real-time control
is an unsolved problem, as far as I know.  True incremental garbage
collection either requires special processor design or is very inefficient,
and the real-time programming people don't like inefficiency, either.
Thus, there are still very important application areas (and real-time
programming is growing in importance) for which garbage collection is
inappropriate.

Many people do not know that it is possible to use a garbage collector
in C++ or C.  Hans Boehm has such a collector, which he developed for
Russel.  I just saw an announcement of a Modula-3 implementation, and
they are using it, so it is pretty general purpose.  This garbage collector
is not fast, because it can make almost no assumptions about the layout of
objects and so must be conservative.  However, the main reason for a garbage
collector in C++ would be to catch "space leaks", so it would not have to
be called very often.

Ralph Johnson