Newsgroups: comp.lang.c++
Path: utzoo!censor!geac!alias!earth!rae
From: Reid Ellis <rae@gpu.utcs.toronto.edu>
Subject: "foo operator+()" vs "foo& operator+()"
	[WAS friend vs member operator+()]
Message-ID: <rae.659300778@earth>
Sender: Reid Ellis <rae%alias@csri.toronto.edu>
Reply-To: Reid Ellis <rae@gpu.utcs.toronto.edu>
Organization: Alias Research, Inc. Toronto ON Canada
References: <11759@hubcap.clemson.edu> <1990Nov21.140621.4229@ssd.kodak.com> <11782@hubcap.clemson.edu> <1990Nov22.001208.26092@athena.mit.edu>
Date: 22 Nov 90 19:06:18 GMT

ahodgson@hstbme.mit.edu (Antony Hodgson) writes:
>Just a warning that the use of the expression:
>
>	foo& operator + ( foo& f )
>or
>	friend foo& operator + ( foo& f1, foo& f2 )
>
>will almost invariably lead to a run-time error. ... 
> ... It's much better to define the operator as
>
>	foo operator+(foo& f)
>
>and let the system deal with deallocating it when it goes out of scope.

If the object if large, it is sometimes desirable to maintain a static
instance within the operator method and return a reference.  e.g.:

	foo & foo::operator+=(const foo &f) { ... }

	foo & foo::operator+(const foo &f)
	{
		static foo sf;

		sf = *this;
		return sf += f;
	}

This is a variation on the standard "use the stack" method of
operator+().  The only way to get "caught" using this is if you hold
the return value in a reference, as in:

	foo &rf = foo1 + foo2;

<Personal Opinion ON>
	I consider this poor form myself.  If you had defined the add
	method as "foo foo::operator+(..)" then you would be creating a
	reference to a temporary.
<Personal Opinion OFF>

						Reid
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