From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gabriel Dos Reis <Gabriel.Dos-Reis@cmla.ens-cachan.fr>
To: gdr@gcc.gnu.org
Cc: gcc-prs@gcc.gnu.org
Subject: Re: c++/3585: wrong function overload resolution?
Date: Fri, 06 Jul 2001 06:56:00 -0000
Message-id: <20010706135601.17299.qmail@sourceware.cygnus.com>
X-SW-Source: 2001-07/msg00159.html
List-Id: <gcc-prs.sourceware.org>

The following reply was made to PR c++/3585; it has been noted by GNATS.

From: Gabriel Dos Reis <Gabriel.Dos-Reis@cmla.ens-cachan.fr>
To: gawrilow@math.tu-berlin.de
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c++/3585: wrong function overload resolution?
Date: 06 Jul 2001 15:49:45 +0200

 gawrilow@math.tu-berlin.de writes:
 
 | >Number:         3585
 | >Category:       c++
 | >Synopsis:       wrong function overload resolution?
 | >Confidential:   no
 | >Severity:       serious
 | >Priority:       medium
 | >Responsible:    unassigned
 | >State:          open
 | >Class:          rejects-legal
 | >Submitter-Id:   net
 | >Arrival-Date:   Fri Jul 06 04:06:01 PDT 2001
 | >Closed-Date:
 | >Last-Modified:
 | >Originator:     Ewgenij Gawrilow
 | >Release:        3.0
 | >Organization:
 | >Environment:
 | Sun UltraSPARC, Solaris 8
 | >Description:
 | Let's consider the following fragment:
 | 
 | void f(int& x) { }  // #1
 | 
 | void f(int x) { }   // #2
 
 Nobody should be writing that :-)
 
 | int temp() { return 0; }
 | 
 | int main() {
 |   int var=0;
 |   f(var);       // should resolve to #1
 
 On what basis?
 
 |   f(temp());    // resolves to #2
 | }
 | 
 | The gcc rejects f(var) as ambiguous reasoning that #1 and #2
 | were equally good.
 
 GCC is right in doing so.
 
 | IMHO, resolving to #2 includes an
 | lvalue-to-rvalue conversion, where #1 incurs an identity
 | conversion, thus being better. Am I missing something?
 
 identity and lvalue-to-rvalue conversion both have Exact Match rank.
 See Table 9.
 
 | Thus the final questions: who understands the overload
 | resolution rules better: gcc 3.0, gcc 2.95,
 
 GCC-3.0.
 
 | How could I otherwise distinct between rvalue and lvalue
 | arguments to an overloaded function, without using
 | f(const T&) ?
 
 You cannot because both lvalue-transformation and identity
 transformation have Exact Match rank.
 
 -- Gaby