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From: perez@csc.ti.com (Edward Perez)
Newsgroups: comp.lang.c++
Subject: Re: reference parameters for overloaded operators
Message-ID: <PEREZ.90Aug27161734@pottawatomie.csc.ti.com>
Date: 27 Aug 90 21:17:34 GMT
Sender: usenet@csc.ti.com (USENET News System)
Distribution: comp.lang.c++
Organization: TI Computer Science Center, Dallas
Lines: 40

In article <56873@microsoft.UUCP> jimad@microsoft.UUCP (Jim ADCOCK) writes:

  The 'Slicing' problem arises in C++ when some "thing2" is passed by
  value as a parameter -- where the exact type of "thing2" is not known,
  because the "thing2" is actually a derivative of some base class "thing."
  But, in deriving thing2, more members are typically added to thing2
  than are in a base class thing.  Passing thing2 by value, as-if it
  were a "thing", causes those extra members not to be copied -- they
  are "sliced off."  This generally leads to undesirable behavior.  The
  solution is simple, once recognized:  "never" use pass-by-value where
  you'd expect polymorphic behavior.  Use [const] references instead.

  ....In the following code, PrintWith_version2 suffers the slicing problem.
  PrintWith_version1 avoids the problem by passing by reference -- effectively
  allowing different sized objects to be used as its parameter.

  <code example deleted>

jim, i understand what you mean by slicing and the problems one could get into.
however, when i compiled the code example using AT&T 2.0 06/30/89, i got the
following output:

thing1_name					<== thing1.Print()
thing2_firstname thing2_lastname		<== thing2.Print()
thing1_name thing2_firstname thing2_lastname	<== thing1.PW_v1(thing2);
thing1_name thing2_firstname thing2_lastname	<== thing1.PW_v2(thing2);

according to your slicing definition, when PrintWith_version2 is called from
main, a temp THING is created using thing2 since thing2 is being passed by
value.  therefore, shouldn't the last line not have "thing2_lastname" because
THING doesnt have a name2 ??  does the fact that the functions are virtual
affect this in any way ??

what do you get when you run your example through your compile <which one>??

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