Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!osu-cis!killer!texbell!sw1e!uucibg
From: uucibg@sw1e.UUCP (3929])
Newsgroups: comp.lang.c++
Subject: Re: Smalltalk-80 like inheritance in C++ possible ?
Message-ID: <1411@sw1e.UUCP>
Date: 23 Mar 89 14:19:25 GMT
References: <110@honold.UUCP> <5481@rlvd.UUCP>
Reply-To: uucibg@sw1e.UUCP (Brian Gilstrap [5-3929])
Organization: Southwestern Bell Telephone Co
Lines: 37

In article <5481@rlvd.UUCP> cmc@inf.rl.ac.uk (Chris Crampton) writes:
>In article <110@honold.UUCP> franco@honold.UUCP (Franco Monti) writes:
>>    How can I translate the behavior of
>>    the code outline [below] to the appropiate structures in C++ ?
>
   [A very good translation from some Smalltalk code to some C++ code]
>Hope this answers your question.

Just a quick note:  While it may be possible to port large portions of many
classes from Smalltalk-like languages to C++, there are some definite problems. 
The biggie is of course the fact that C++ uses strong typing of objects (e.g.
determine at compile time what function/method is to be invoked ) while
Smalltalk and Smalltalk-like languages use weak typing of objects and actually
accomplish function address resolution at run-time.  The net result of this is
that in Smalltalk-like languages you can try to invoke any method of (send any
message to/ invoke any member function of) any object.  If the object's class
doesn't implment the method (message/function) then the method (function/
essage) resolution code will detect such a condition.  The resolution code will
then often invoke the object's "error" method (send the error message/invoke
the error function).

In a nutshell:  In Smalltalk-like languages, class references (refs to objects)
are not typed and you can send them any message you want to.  In C++-like 
languages (or Eiffel-like languages, etc.), references to objects are typed
and you can only send a message to an object (invoke an object's function) if
the object's class definition included mention of that message (method,
function).

I'd be interested to discuss the plusses/minuses of each approach here or
in comp.misc or comp.compilers or where ever seems appropriate.  But please,
no flames, though corrections would be appreciated.

Brian R. Gilstrap                          Southwestern Bell Telephone
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