Xref: utzoo comp.lang.c++:6130 gnu.g++:594
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!nih-csl!keith
From: keith@nih-csl.UUCP (keith gorlen)
Newsgroups: comp.lang.c++,gnu.g++
Subject: Re: function modifiers
Summary: I think this must be a g++ bug
Message-ID: <1310@nih-csl.UUCP>
Date: 14 Jan 90 04:48:22 GMT
References: <14940@robin.cs.nott.ac.uk>
Organization: NIH-CSL, Bethesda, MD
Lines: 39

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 of the
> following form:
> 
> 	  const Object* Object::method() const;
> 
> and also:
> 
>           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. 

In C++ 2.0, you can overload member functions based on their
const-ness; i.e., you can declare a const member function that has the
same name and arguments as a non-const member function.  This is very
useful.  Consider:

class String {
// ...
	char& operator[](int);
	const char& operator[](int) const;
};
// ...
	const String s = "A constant string";
	String t = "A variable string";
	t[1] = 'x';		// OK -- t[1] calls String::operator[](int), which returns a char&
	char z = s[1];		// OK -- s[1] calls String::operator[](int) const, which returns a const char&
	s[1] = 'x';		// Error -- can't assign to a const

If you want to make a const member function a friend, you must be able
to specify the const modifier in the friend declaration to uniquely
identify it, since it may be overloaded in this fashion.
-- 
	Keith Gorlen			phone: (301) 496-1111
	Building 12A, Room 2033		uucp: uunet!nih-csl!keith
	National Institutes of Health	Internet: keith@alw.nih.gov
	Bethesda, MD 20892