From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-332931-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 27404 invoked by alias); 4 Oct 2010 08:11:15 -0000
Received: (qmail 27390 invoked by uid 22791); 4 Oct 2010 08:11:13 -0000
X-SWARE-Spam-Status: No, hits=-2.3 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00,MISSING_MID
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 04 Oct 2010 08:11:09 +0000
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/45873] Parameter packs not expanding consistently in function return types
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
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: Known to fail
In-Reply-To: <bug-45873-4@http.gcc.gnu.org/bugzilla/>
References: <bug-45873-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Date: Mon, 04 Oct 2010 08:11:00 -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
X-SW-Source: 2010-10/txt/msg00320.txt.bz2
Message-ID: <20101004081100.VDD9QR2HEv_tf0EayaarQUxNgAJ9c7Rvqm8LeGVPbRM@z>

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45873

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.4.3, 4.5.1, 4.6.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2010-10-04 08:11:07 UTC ---
(You didn't say which version this PR is for, although it doesn't work with any
I tried)

Here's a self-contained testcase, with a fix so the workaround actually works
(it was missing the template argument on baz<pair>)

template<class, class>
struct pair
{
    template<class T1, class U1>
        pair(T1&& t, U1&& u) { }
};

template <template <class ...> class T, class ...Args>
auto foo(Args... args) -> T<Args...>
{ return T<Args...>(args...); }

template <template <class ...> class T, class ...Args>
auto bar(Args... args) -> T<int, double>
{ return T<Args...>(args...); }


// The following work-around seems to work:
template <template <class ...> class T, class ...Args> struct expand
{ typedef T<Args...> type; };

template <template <class ...> class T, class ...Args>
auto baz(Args... args) -> typename expand<T, Args...>::type
{ return T<Args...>(args...); }


int main()
{
   // error: no matching function for call to 'foo(int, double)'
   foo<pair>(1, 2.0);
   bar<pair>(1, 2.0); // OK, returns pair<int, double>
   baz<pair>(1, 2.0); // OK, returns pair<int, double>
}


I think deduction fails for foo<pair>(1, 2.0), though I'm not sure if it
should.

For baz<pair> deduction succeeds, the template parameters appear in a
nested-name-specifier which is a non-deduced context.