Path: utzoo!utgpu!water!watmath!clyde!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c++
Subject: Re: Declaration of multi-dimensional arrays.
Message-ID: <7449@haddock.ima.isc.com>
Date: 14 Sep 88 16:53:56 GMT
References: <8809032205.aa09007@PARIS.ICS.UCI.EDU> <8166@alice.UUCP>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 28

In article <8166@alice.UUCP> bs@alice.UUCP (Bjarne Stroustrup) writes:
>[Douglas C. Schmidt asks about providing multi-dimensional arrays via
>overloading the subscript operator instead of the function-call operator]
>
>I think that an array with multiple dimentions, such as a Fortran
>a(1,2,3), or a C++ array accessed (through a dope-vector or something)
>using an overloaded operator(): a(1,2,3), is different in several
>ways from the C array you get by repeated use of subscripting v[1][2][3].

Certainly.  And a `+' meaning string concatenate is different from the `+'
meaning integer add.  But it can still be convenient to use the same symbol.
(In fact, I might want to overload *both* a[1,2,3] and a(1,2,3) with different
semantics, for some classes where this would make sense.)

>On the other hand, overloading operator[] to take more than one
>``sunbcript argument'' runs into a problem with C.  a[1,2,3] is
>perfectly legal C and C++ (provided a is of a suitable type).

I don't find this a compelling argument.  I doubt that any serious program
uses this `perfectly legal' feature, and little would be lost if it had to be
written a[(1,2,3)] to force the comma operator.  (This is analogous to the
situation for function calls.)  To keep the grammar simple, this should apply
to all uses of the [] operator, overloaded or not.

I'll bet allowing `a[1,2,3]' would break less code than changing the meaning
of `int f();' did.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint