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From: "daniel.kruegler at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/57172] New: [C++11][DR 1164] Template overload resolution ambiguous for T&& versus T&
Date: Sat, 04 May 2013 19:38:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57172

             Bug #: 57172
           Summary: [C++11][DR 1164] Template overload resolution
                    ambiguous for T&& versus T&
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


The following code is rejected by gcc 4.9.0 20130428 (experimental) using the
compiler flags

-std=c++11 -Wall -pedantic-errors

//-----------------------------
template<typename T> int f(T&){}
template<typename T> int f(T&&);
int i;
int j = f(i);
//-----------------------------

"main.cpp|4|error: call of overloaded 'f(int&)' is ambiguous|
 main.cpp|4|note: candidates are:|
 main.cpp|1|note: int f(T&) [with T = int]|
 main.cpp|2|note: int f(T&&) [with T = int&]|"

This example was relevant for

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1164

and the core language has been adapted to make it well-formed as described by
[temp.deduct.partial] p9 b1. The compiler should select the first overload
here.