Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!microsoft!jimad
From: jimad@microsoft.UUCP (Jim ADCOCK)
Newsgroups: comp.lang.c++
Subject: Re: more on "foo & operator+ (const foo&)"
Message-ID: <59617@microsoft.UUCP>
Date: 6 Dec 90 20:18:43 GMT
References: <11759@hubcap.clemson.edu| <1939@m1.cs.man.ac.uk> <fuchs.659473943@t500m0> <rae.659684428@earth>
Reply-To: jimad@microsoft.UUCP (Jim ADCOCK)
Organization: Microsoft Corp., Redmond WA
Lines: 33

In article <rae.659684428@earth| Reid Ellis <rae@gpu.utcs.toronto.edu> writes:
|Only if your operator+() assumed that none of the parameters could
|ever be the result of a previous addition.  I agree that this
|technique should be avoided if possible, but if you need the speed,
|you can do it if you're careful.  e.g., for an integer class "Tint":
|
|Tint& operator+(const Tint &left, const Tint &right)
|{
|	static Tint stat;
|
|	stat.value = left.value + right.value;
|	return stat;
|}
|
|This will never have a problem with either of 'l' or 'r' being the
|result of a previous '+' -- i.e., a reference to 's'.
|
|But I should state again that I agree that this should be avoided if
|possible.  Be sure that doing this will really speed up your code by
|profiling it before introducing something that could cause subtle
|errors.

??? I guess I don't understand what you're suggesting.  The above example
has [IMHO] unsubtle problems, consider:

	Tint a=100, b=200, c=300, d=400, e;
	e = (a + b) + (c + d);
	e.print();

results in 600 on my compiler [your compiler might give a different 
answer -- but its unlikely to be the 'right' one!]

Or is this what you mean by "subtle errors" ?


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