Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ira.uka.de!fuchs
From: fuchs@it.uka.de (Harald Fuchs)
Newsgroups: comp.lang.c++
Subject: Re: operator[]
Keywords: array C++ overloaded
Message-ID: <fuchs.656622010@t5000>
Date: 22 Oct 90 19:00:10 GMT
References: <1442@ziggy.EDU>
Sender: news@ira.uka.de (USENET News System)
Organization: University of Karlsruhe, FRG
Lines: 31

card@ziggy.EDU (James Card) writes:
>Is there any way of telling which side of the '=' a class []
>operator is on?  I was thinking of a possible application in which
>a disk file could be used as a virtual array.  A constructor could
>be used to open the "virtual" array and a destructor would be used
>to close the "virtual" array.  Using this scheme, object[] operations
>appearing on the left hand side of the '=' would cause a write to the
>associated file, and object[] appearing on the right hand side of the
>'=' would cause a read of the disk array.

class file;

class fileref {
  friend file;
  file& f;
  unsigned long ix;
  fileref (file& ff, unsigned long i): f (ff), ix (i) {}
public:
  fileref& operator= (char);    // left hand side
  operator char ();             // right hand side
};

class file {
public:
  file (const char* name);
  ~file ();
  fileref operator[] (unsigned long ix) { return fileref (*this, ix); }
};
--

Harald Fuchs <fuchs@it.uka.de> <fuchs%it.uka.de@relay.cs.net> ...