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From: hopper@omnifarious.mn.org (Eric M. Hopper)
Subject: Re: overload operator sizeof
Date: 1996/11/17
Message-ID: <x23ey8hcd2.fsf@omnifarious.omnifarious.mn.org>#1/1
X-Deja-AN: 197075301
references: <VpdjyEpfhy5I090yn@nada.kth.se>
x-original-date: 17 Nov 1996 11:15:21 -0600
organization: Omnifarious Software
x-auth: PGPMoose V1.1 PGP comp.std.c++
newsgroups: comp.std.c++


d96-mst@nada.kth.se (Mikael Steldal) writes:

>  Has anyone considered if it would be good to allow overloading of
> operator sizeof? I.e.
>  class foo {
>     // ...  char* buffer; size_t bufsize;
>  public:
>     size_t operator sizeof(void) { return bufsize; } // ...
> };
>  For a string, the overloaded operator sizeof could return the same as
> capacity().
>  Then we could also allow the use of ::operator sizeof to always get
> the real size of the object.

	I don't think this would add a great deal to the language.

	sizeof has historically been used for only two purposes.  One
is, finding out the size of a data structure so you could allocate
memory for it.  The other is compile-time determination of the number of
elments in an array without going to the trouble of using a #define or
const declaration.

	The use of sizeof that you propose doesn't leverage either of
those prior uses to reduce the mental burden on the programmer.

	sizeof DOES have vague connations of 'actual storage used',
which your new use does leverage, but the cost of the syntatic sugar
would be too high.

	Most code currently using sizeof is critical code that heavily
depends on sizeof's standard meaning in order to function.  If someone
adds a sizeof operator to a class, all that code breaks and has to be
re-written to use ::operator sizeof.

	Also, adding a new overloadable operator increases the amount of
things you have to think about and remember when you're reading code.

	One interesting change to sizeof that I could think of would be
making it return the 'right' value for a derived class in the presence
of RTTI, although I suspect that that proposal also has a number of
problems.

--
--Eric Hopper
He who joyfully marches to music in rank and file has
already earned my contempt.  He has been given a large brain by mistake,
since for him the spinal cord would suffice.  - Mark Twain
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