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From: mark@tove.UUCP (Mark Weiser)
Newsgroups: net.lang,net.lang.st80
Subject: Re: What is Object-Oriented
Message-ID: <117@tove.UUCP>
Date: Tue, 5-Feb-85 19:40:23 EST
Article-I.D.: tove.117
Posted: Tue Feb  5 19:40:23 1985
Date-Received: Sun, 10-Feb-85 03:36:06 EST
References: <3013@umcp-cs.UUCP>
Reply-To: mark@tove.UUCP (Mark Weiser)
Organization: U of Maryland, Laboratory for Parallel Computation, C.P., MD
Lines: 35
Xref: watmath net.lang:1398 net.lang.st80:183

In article <3013@umcp-cs.UUCP> koved@umcp-cs.UUCP (Larry Koved) writes:
>There are languages which use overloading and/or inheritence, but
>are not OO, and visa versa.

I'd be interested in an example of inheritence without OO.  What one
inherits in OO is operators and local variables.  Is there something
else to inherit?

>Finally, it should also be noted that there are different degrees of
>being OO.  Smalltalk is almost at one extreme, while Modula-2 is almost
>at the other extreme.  

Not Fortran or Forth at the other extreme?  Modula-2?  Do you mean
there are different KINDS of OO, with Modula-2 and Smalltalk being
prototypical examples, or do you really mean degrees?

>The performance of the language (instructions
>per second) is a major consideration in deciding the degree to which
>a language's design is OO.  Being extremely OO is expensive in
>processing time and/or space.

Now this is an interesting issue.  Why should OO be expensive?
It need not be, because it need not be a runtime feature of a language.
Smalltalk is mostly interpreted, and so is slow for that reason,
not because it is OO.  The Maryland Flavors Package under Franz
Lisp allows compiled methods, flavors etc, and so runs not too
much slower than bare Lisp.  And a completely statically checked
and implemented OO language should be as fast as any other at runtime.
(Is c++ something like this?  I'm not sure.)
Might be slow to compile with current technology--but we haven't had
much practice at building fast OO compilers.
-- 
Spoken: Mark Weiser 	ARPA:	mark@maryland	Phone: +1-301-454-7817
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