NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/comp/lang/cplus/15958

Text File | 1992-11-09 | 1.7 KB | 53 lines

Newsgroups: comp.lang.c++
Path: sparky!uunet!fmrco!pandrews!pandrews
From: [e-mail] (Paul Andrews)
Subject: Re: operator [][]
Message-ID: <[e-mail]>
Sender: [e-mail]
Reply-To: [e-mail]
Organization: Fidelity Investments Ltd.
References: <[e-mail]>
Date: Mon, 9 Nov 1992 09:53:52 GMT
Lines: 40

In article [e-mail], [e-mail] (Duanyang Guo) writes:
> for multiple dimension array, is it possible to define
> an operator [][](say for two dimensions)? I try to define
> it as
> int & operator[][] (int, int);
>
> which g++ complains about it.
>
> any idea or just sth is wrong with my try?
>
You can only overload single []. Remember though that this generates a function call
like:
    <class>.operator[](<arg>)

which returns a value. So make that value be a reference to another class which also
has an operator[] overload. Then when you specify:

    <classA>[<arg1>][<arg2>]

you will actually get

    <classA>.operator[](<arg1>).<classB>.operator[](<arg2>)

classB should now call a well-known function in classA to indicate what argument was
passed to it. A good way of doing this is for classA to inherit yet another class
(classC!) which has a well-known virtual function which classA overrides. That way
both classC and classB can be re-used whenever you want to have multiple [].

Simple huh?

(apologies if the syntax of the expanded function calls isn't quite correct).

(I would be interested to know if anyone has any other ways of doing this).

(Is there any standard nomenclature for classes like C and B above? something like
classB is a slave class, classC is a functor or what?)

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Paul Andrews