From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-410426-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 32645 invoked by alias); 20 Dec 2012 18:36:29 -0000
Received: (qmail 30153 invoked by uid 48); 20 Dec 2012 18:36:08 -0000
From: "leonid at volnitsky dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/55766] New: temlate alias is not equivalent (const-ness is not recognized)
Date: Thu, 20 Dec 2012 18:36:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: leonid at volnitsky dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-55766-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
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
X-SW-Source: 2012-12/txt/msg02034.txt.bz2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D55766

             Bug #: 55766
           Summary: temlate alias is not equivalent (const-ness is not
                    recognized)
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: leonid@volnitsky.com


Created attachment 29016
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=3D29016
goog.ii

I have following alias in my code:

    template<bool Cnd, class T=3Dvoid>=20=20
    using  eIF =3D typename std::enable_if <Cnd,T>::type;

I encountered code where alias is not equivalent to direct use of enable_if.

Attached are good.ii (with enable_if) which both GCC480-20121220 and CLANG32
can compile, and bad.ii (with alias eIF), which only CLANG can compile.=20


    diff good.ii bad.ii

    80517c80517
    <   typename std::enable_if<(sizeof(Arg1),N=3D=3D1), Arg1>::type
    ---
    >   eIF<(sizeof(Arg1),N=3D=3D1), Arg1>
    80522c80522
    <   typename std::enable_if<(sizeof(Arg1),N=3D=3D2), Arg2>::type
    ---
    >   eIF<(sizeof(Arg1), N=3D=3D2), Arg2>

Comma op in expression (sizeof(Arg1),N=3D=3D1) used to makes templated memb=
er
function depend on Arg1 template argument (to trigger SFINAE).=20

Error message:

lambda.h:45:2: error: integral expression =E2=80=98(0, false)=E2=80=99 is n=
ot constant