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From: david@smythsun.JPL.NASA.GOV (David Smyth)
Newsgroups: comp.lang.c++
Subject: Re: Generating temporaries
Message-ID: <4799@jpl-devvax.JPL.NASA.GOV>
Date: 14 Apr 89 19:12:10 GMT
References: <8904042239.AA07890@yahi.stanford.edu> <6590094@hplsla.HP.COM>
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Organization: Jet Propulsion Laboratory, Pasadena, CA.
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In article <6590094@hplsla.HP.COM> jima@hplsla.HP.COM (Jim Adcock) writes:
**************************************************************************
*> While far from simple, or easy, ... avoids generating unnecessary
*> copies or temporaries, and generates fast, compact code.
*> 
*> The general approach is to have the binary operators, instead of
*> returning a "Matrix", return a linked structure that represents ...
*> 
*> For example:
*> 
*> a = b + c + d;
*> 
*> where a, b, c, and d are matrices, results in 11 machine code
*> instructions that set up a linked structure saying what needs to get
*> added to what, and where to put the results, followed by one call to a
*> routine that copies b into a (resizing if necessary), and then adds c
*> to a, then adds d to a.
*> 
*> It seems if you mix adds and multiplies in an expression you are forced
*> to generate a temporary [on heap space] which then must be reclaimed at
*> destruction time.
*> 
*> If anybody has actually figured out a cleaner way to handle these
*> difficult large, variable sized object classes, please tell us.
**************************************************************************

One way the is easy: DO NOT DEFINE OR USE OPERATORS FOR CLASSES!

What your approach is doing is a hidden building of messages which is
then given to the assignment method.  That is, as you pointed out, "far
from simple, or easy."

**** flame on ****
Supposedly, we are using C++ to make our lives simpler so we are more
productive.  This approach, as well as other binary operator
approaches, are simply not leading to that goal.
**** flame off ****

Methods are simple, operators are hard.  Therefore, forget the
operators, don't try to write code which looks like C, and then you
WILL see productivity improvements.