[Bug libstdc++/67566] <string> std::move is in global scope g++ 5.1 -std=c++14

[Bug libstdc++/67566] <string> std::move is in global scope g++ 5.1 -std=c++14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67566

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
std::move is declared in namespace std as required by the C++ standard. It is
found by ADL. This is not a bug.

[Bug libstdc++/67566] <string> std::move is in global scope g++ 5.1 -std=c++14

[forest_software at mail dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67566

--- Comment #2 from Roman Koptev <forest_software at mail dot ru> ---
I've installed gcc 5.1 from repository
http://ppa.launchpad.net/ubuntu-toolchain-r/ppa/ubuntu on Ubuntu Studio:

lsb_release -a
LSB Version:   
core-2.0-amd64:core-2.0-noarch:core-3.0-amd64:core-3.0-noarch:core-3.1-amd64:core-3.1-noarch:core-3.2-amd64:core-3.2-noarch:core-4.0-amd64:core-4.0-noarch:core-4.1-amd64:core-4.1-noarch:security-4.0-amd64:security-4.0-noarch:security-4.1-amd64:security-4.1-noarch
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.3 LTS
Release:        14.04
Codename:       trusty

g++ --version
g++ (Ubuntu 5.1.0-0ubuntu11~14.04.1) 5.1.0
Copyright (C) 2015 Free Software Foundation, Inc.
Это свободно распространяемое программное обеспечение. Условия копирования
приведены в исходных текстах. Без гарантии каких-либо качеств, включая 
коммерческую ценность и применимость для каких-либо целей.

For the program above (main.cpp):

#include <string>
#include <boost/move/move.hpp>

using boost::move;

main()
{
  std::string a = "fff";
  std::string b = move(a);
}

Compile as:
g++ main.cpp -std=c++14

I have the output (ambiguous call of overloaded function, Sorry for russian
localization):

main.cpp: В функции «int main()»:
main.cpp:9:25: ошибка: вызов перегруженной функции «move(std::string&)»
неоднозначен
   std::string b = move(a);
                         ^
In file included from /usr/include/boost/move/utility.hpp:28:0,
                 from /usr/include/boost/move/move.hpp:29,
                 from main.cpp:2:
/usr/include/boost/move/utility_core.hpp:211:77: замечание: candidate: typename
boost::move_detail::remove_reference<T>::type&& boost::move(T&&) [with T =
std::basic_string<char>&; typename
boost::move_detail::remove_reference<T>::type = std::basic_string<char>]
          inline typename ::boost::move_detail::remove_reference<T>::type &&
move(T&& t) BOOST_NOEXCEPT
                                                                             ^
In file included from /usr/include/c++/5/bits/stl_pair.h:59:0,
                 from /usr/include/c++/5/bits/stl_algobase.h:64,
                 from /usr/include/c++/5/bits/char_traits.h:39,
                 from /usr/include/c++/5/string:40,
                 from main.cpp:1:
/usr/include/c++/5/bits/move.h:101:5: замечание: candidate: constexpr typename
std::remove_reference< <template-parameter-1-1> >::type&& std::move(_Tp&&)
[with _Tp = std::basic_string<char>&; typename std::remove_reference<
<template-parameter-1-1> >::type = std::basic_string<char>]
     move(_Tp&& __t) noexcept
     ^

Now for simple program (main.cpp):

#include <string>

main()
{
  std::string a = "fff";
  std::string b = move(a);
}

Compile with:
g++ main.cpp

I have the correct error message (no declaration move in this scope):

main.cpp: В функции «int main()»:
main.cpp:6:25: ошибка: нет декларации «move» в этой области видимости
   std::string b = move(a);
                         ^

But if I compile as:
g++ main.cpp -std=c++14

It compile successfully and has no any output on stdout or stderr

That'is if I compile any program with the option -std=c++14, after including
<string> (may be and other headers) std::move surely and always is in global
namespace, available without std:: or using std or using std::move and this is
surely abnormal.
>From gcc-bugs-return-497178-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Mon Sep 14 12:11:51 2015
Return-Path: <gcc-bugs-return-497178-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Delivered-To: listarch-gcc-bugs@gcc.gnu.org
Received: (qmail 74964 invoked by alias); 14 Sep 2015 12:11:51 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Delivered-To: mailing list gcc-bugs@gcc.gnu.org
Received: (qmail 74906 invoked by uid 48); 14 Sep 2015 12:11:47 -0000
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/67566] <string> std::move is in global scope g++ 5.1 -std=c++14
Date: Mon, 14 Sep 2015 12:11:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 5.1.0
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: RESOLVED
X-Bugzilla-Resolution: INVALID
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields:
Message-ID: <bug-67566-4-tUm8pBKbXc@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-67566-4@http.gcc.gnu.org/bugzilla/>
References: <bug-67566-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-09/txt/msg01156.txt.bz2
Content-length: 801

https://gcc.gnu.org/bugzilla/show_bug.cgi?idg566

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Roman Koptev from comment #2)
> That'is if I compile any program with the option -std=c++14, after including
> <string> (may be and other headers) std::move surely and always is in global
> namespace, available without std:: or using std or using std::move and this
> is surely abnormal.

No it isn't in the global namespace, it's in namespace std as required by the
C++ standard. What's happening is called Argument Dependent Lookup and is
perfectly normal.

http://en.cppreference.com/w/cpp/language/adl
https://en.wikipedia.org/wiki/Argument-dependent_name_lookup
http://stackoverflow.com/questions/8111677/what-is-argument-dependent-lookup-aka-adl-or-koenig-lookup