Xref: utzoo comp.lang.c++:6061 gnu.g++:588
Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!utoday!comeau
From: comeau@utoday.UUCP (Greg Comeau)
Newsgroups: comp.lang.c++,gnu.g++
Subject: Re: function modifiers
Message-ID: <1141@utoday.UUCP>
Date: 10 Jan 90 16:33:33 GMT
References: <14940@robin.cs.nott.ac.uk>
Reply-To: comeau@.UUCP (Greg Comeau)
Organization: UNIX Today!, Manhasset, NY
Lines: 30

In article <14940@robin.cs.nott.ac.uk> gas@cs.nott.ac.uk (Alan Shepherd) writes:
>In the code for the NIH library, there are several declarations ...:
>	  const Object* Object::method() const;
>          friend const Object* Object::method() const;
>
>I've tried to compile this with g++-1.36.2 and discovered that friends
>aren't allowed to have function modifiers in g++ i.e the terminating const. 
>Removing the terminating const causes lots of other related error messages
>to do with const member functions calling non-const member functions etc.
>
>Alan Shepherd

This is correct.  The thing is a const member function can be used with
both const data and non-const data, however a non-const member function can
only be used with non-const data so removing the const means that any
const object that was being manipulated by the previous const function
can no longer be manipulated (where manipulated is really == modified)
since it must maintain the semantics of operations performed on const
data whether that data be member data or non-member data (say an external
global const instance of a class).

So since NIH is working code though, removing the const means that
when a const MF calls a non-const MF it has no way to keep track of what
the non-const function is doing.  In cfront 2.0 this produces a warning
though and not an error.
-- 
Greg, Comeau Computing, 91-34 120th Street, Richmond Hill, NY, 11418
Also, mag writer for UNIX Today! (SysAdm columnist), Microsoft Systems Journal
(C programming), + others. Also, BIX c.language & c.plus.plus conf. moderator.
Here:attmail!csanta!greg / BIX:comeau / CIS:72331, 3421 / voice:718-849-2355