[Bug c++/48424] New: C++0x parameter packs expansion problem

[Bug c++/48424] New: C++0x parameter packs expansion problem

[aiedail92 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

           Summary: C++0x parameter packs expansion problem
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: aiedail92@gmail.com


The following testcase, which should be valid (at least I think so), fails to
compile:


#include <tuple>
#include <functional>

template<typename... T>
struct test
{
    std::tuple<int, T..., long> t;          // OK
    void(*fptr)(int, T..., long);           // Error (1)
    std::function<void(int, T..., long)> f; // Error (2)
};


Since in (1) and (2) T... is not a parameter pack declaration, but a parameter
pack expansion, shouldn't the code be valid? And if it's really not valid, is
there a good explanation for this?


luca@laptop-luca:~$ g++ --version
g++ (GCC) 4.7.0 20110330 (experimental)

luca@laptop-luca:~$ g++ -std=c++0x testcase.cc 
testcase.cc:8:32: error: parameter packs must be at the end of the parameter
list
testcase.cc:9:39: error: parameter packs must be at the end of the parameter
list

[Bug c++/48424] C++0x parameter packs expansion problem

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-04-03 15:13:50 UTC ---
It certainly looks reasonable. Jason, should this be accepted?

[Bug c++/48424] C++0x parameter packs expansion problem

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.04.04 18:16:41
     Ever Confirmed|0                           |1

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2011-04-04 18:16:41 UTC ---
Yes, that's an obsolete restriction that has been removed from the draft;
8.3.5/13 used to say "A function parameter pack, if present, shall occur at the
end of the parameter-declaration-list." but it doesn't any more.

[Bug c++/48424] C++0x parameter packs expansion problem

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-04-18 21:23:46 UTC ---
Jason, when this bug is fixed will this be allowed too?

template<typename... Args1>
struct S
{
  template<typename... Args2>
    void f(Args1... args1, Args2&&... args2)
    {
    }
};

S<int, int> s;

Currently this gives:

var.cc:5:47: error: parameter packs must be at the end of the parameter list

But it seems like it should be ok since sizeof...(Args1) is fixed when calling
S::f and so shouldn't interfere with deducing Args2

(I wanted to do something of this form to make std::mem_fn support varargs
member functions such as R (T::*)(int, ...) where Args1 would be [int] and
Args2 would be the additional arguments passed to _Mem_fn::operator())

[Bug c++/48424] C++0x parameter packs expansion problem

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> 2011-04-18 22:45:55 UTC ---
Yes, that looks OK too.

[Bug c++/48424] C++0x parameter packs expansion problem

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |

[Bug c++/48424] C++0x parameter packs expansion problem

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-26 13:22:54 UTC ---
Author: jason
Date: Thu May 26 13:22:51 2011
New Revision: 174285

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174285
Log:
    PR c++/48424
    * decl.c (grokparms): Function parameter packs don't need to
    go at the end.
    * pt.c (type_unification_real): But they aren't deduced otherwise.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic111.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic41.C

[Bug c++/48424] C++0x parameter packs expansion problem

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.1

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-26 13:44:06 UTC ---
Fixed for 4.6.1.

[Bug c++/48424] C++0x parameter packs expansion problem

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48424

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-26 13:44:26 UTC ---
Author: jason
Date: Thu May 26 13:44:20 2011
New Revision: 174287

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174287
Log:
    PR c++/48424
    * decl.c (grokparms): Function parameter packs don't need to
    go at the end.
    * pt.c (type_unification_real): But they aren't deduced otherwise.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/variadic111.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/decl.c
    branches/gcc-4_6-branch/gcc/cp/pt.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/variadic41.C