[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

Dodji Seketeli <dodji at gcc dot gnu.org> changed:

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

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[3dw4rd at verizon dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

Ed Smith-Rowland <3dw4rd at verizon dot net> changed:

           What    |Removed                     |Added
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                 CC|                            |3dw4rd at verizon dot net

--- Comment #13 from Ed Smith-Rowland <3dw4rd at verizon dot net> 2011-05-20 16:55:48 UTC ---
I this supposed to work too?

//  This is going to be a variadic array.
#include <cstddef>
#include <type_traits>

template<typename T, std::size_t Dim, std::size_t... Dims>
  struct tensor
  {
  public:
    typedef std::conditional<sizeof...(Dims) == 0, T, tensor<T, Dims...>>
_Elem;
    _Elem elem[Dim]; // (Dim == 0 ? 1 : Dim) like array?
  };

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[tristan.wibberley at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

--- Comment #14 from Tristan Wibberley <tristan.wibberley at gmail dot com> 2011-05-20 19:30:15 UTC ---
Ed,

It depends on the rest of your program that you cut out. As given, no it's
not supposed to work.

see http://gcc.gnu.org/bugs/ for how to report your problem if you have a
good reason to think there's a bug. But for help with c++ you need to go
elsewhere for example the ##c++ chatroom on IRC chat as detailed at
http://freenode.net/

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

Dodji Seketeli <dodji at gcc dot gnu.org> changed:

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

--- Comment #15 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-09-27 14:46:22 UTC ---
Unassigning myself as I am not working on this right now.

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

--- Comment #16 from Jason Merrill <jason at gcc dot gnu.org> 2011-10-02 21:45:08 UTC ---
Author: jason
Date: Sun Oct  2 21:45:01 2011
New Revision: 179436

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=179436
Log:
    PR c++/35722
    Implement N2555 (expanding pack expansion to fixed parm list)
    * pt.c (coerce_template_parms): Allow expanding a pack expansion
    to a fixed-length argument list.
    (unify_pack_expansion): Handle explicit args properly.
    (unify) [TREE_VEC]: Handle pack expansions here.
    [TYPE_ARGUMENT_PACK]: Not here.
    (tsubst_pack_expansion): Don't try to do partial substitution.
    (pack_deducible_p): New.
    (fn_type_unification): Use it.
    (find_parameter_packs_r): Take the TYPE_MAIN_VARIANT
    of a type parameter.
    (check_non_deducible_conversion): Split from type_unification_real.
    (unify_one_argument): Split from type_unification_real...
    (unify_pack_expansion): ...and here.  Drop call_args_p parm.
    (type_unification_real, unify, more_specialized_fn): Adjust.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic-explicit1.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic-nondeduce1.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic117.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic118.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic105.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic35.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic65.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic82.C
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic83.C
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/testsuite/util/testsuite_tr1.h

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
   Target Milestone|---                         |4.7.0

--- Comment #17 from Jason Merrill <jason at gcc dot gnu.org> 2011-10-02 21:53:23 UTC ---
Fixed for 4.7.

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lcid-fire at gmx dot net

--- Comment #18 from Jason Merrill <jason at gcc dot gnu.org> 2011-10-14 19:16:25 UTC ---
*** Bug 50140 has been marked as a duplicate of this bug. ***

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sausage at tehsausage dot
                   |                            |com

--- Comment #19 from Jason Merrill <jason at gcc dot gnu.org> 2012-04-16 02:10:37 UTC ---
*** Bug 45873 has been marked as a duplicate of this bug. ***

[Bug c++/35722] New: [C++0x] Variadic templates expansion into non-variadic class template

[dgregor at gcc dot gnu dot org]

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The following well-formed example produces the incorrect error:

  error: cannot expand ‘G ...’ into a fixed-length argument list

template<typename G = void, typename H = void>
struct foo
{};

template<typename... G>
struct bar : foo<G...>
{};

int main() {
  bar<int, float> f;
}


-- 
           Summary: [C++0x] Variadic templates expansion into non-variadic
                    class template
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dgregor at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[dgregor at gcc dot gnu dot org]

-- 

dgregor at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |dgregor at gcc dot gnu dot
                   |dot org                     |org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-03-27 17:31:52
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu dot org]

-- 

jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu dot org]

------- Comment #1 from jason at gcc dot gnu dot org  2009-01-06 19:47 -------
This was ill-formed under the proposal that was initially adopted, but was made
well-formed in the March 2008 working paper when the following wording was
struck from the end of 14.3:

A template-argument pack expansion shall not occur in a simple-template-id
whose template-name refers to a class template unless the
template-parameter-list of that class template declares a template parameter
pack.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu dot org]

------- Comment #2 from jason at gcc dot gnu dot org  2009-01-07 00:06 -------
This was part of the incorporation of N2555
(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2555.pdf) into the
WP.


-- 

jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[sebor at roguewave dot com]

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------- Comment #3 from sebor at roguewave dot com  2009-04-04 23:12 -------
This limitation makes implementing the latest std::tuple difficult. Quoting
from a post to c++std-lib@accu.org:

Martin Sebor wrote:
> To: C++ libraries mailing list
> Message c++std-lib-23549
> 
> After reducing the error to a smaller test case and some digging
> through gcc Bugzilla it looks as though it is well-formed but gcc
> doesn't implement it yet:
> 
>   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722
> 
> The errors are different but the problem seems the same in both
> cases.
> 
> Martin Sebor wrote:
>> To: C++ libraries mailing list
>> Message c++std-lib-23548
>>
>> I'm probably missing something but can someone confirm that the
>> declaration of the tuple ctor below (taken from N2857) is well
>> formed given that pair is not a variadic template?
>>
>> The latest gcc complains:
>>
>>   error: wrong number of template arguments (1, should be 2)
>>
>> Thanks!
>>
>>   template <VariableType... Types>
>>   class tuple
>>   {
>>   public:
>>     ...
>>     template <Allocator Alloc, class... UTypes>
>>     requires ConstructibleWithAllocator<Types, Alloc, const UTypes&>...
>>     tuple(allocator_arg_t, const Alloc& a, const pair<UTypes...>&);
>>     ...
>>   };
>>
>>
>> Here's a small test case:
>>
>> $ cat t.C && g++ -std=c++0x t.C
>> template <class T, class U> struct pair { };
>> struct allocator_arg_t { };
>> template <class ...T>
>> struct tuple {
>>     template <class U, class ...V>
>>     tuple (allocator_arg_t, const U&, const pair<V...>&);
>> };
>> t.C:6: error: wrong number of template arguments (1, should be 2)
>> t.C:1: error: provided for ‘template<class T, class U> struct pair’


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu dot org]

------- Comment #4 from jason at gcc dot gnu dot org  2009-04-05 04:20 -------
I agree that the working paper says that this should work, but I'm not sure why
the language should specify the use of variadics there; why not

     template <Allocator Alloc, class First, class Second>
     requires ConstructibleWithAllocator<Types, Alloc, const First&>
       && ConstructibleWithAllocator<Types, Alloc, const Second&>
     tuple(allocator_arg_t, const Alloc& a, const pair<First, Second>&);

instead?  The n2555 fix is needed for template template parameters, but in
cases like this where we know what template we're dealing with I don't see why
it's a problem to just pass in the right number of arguments.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[sebor at roguewave dot com]

------- Comment #5 from sebor at roguewave dot com  2009-04-05 14:20 -------
(In reply to comment #4)

The change was introduced in N2622:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2622.pdf

I couldn't find a rationale for the change. Doug might remember


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[sebor at roguewave dot com]

------- Comment #6 from sebor at roguewave dot com  2009-04-05 17:12 -------
See also bug 39642 and bug 39653.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jason at gcc dot gnu dot org]

------- Comment #7 from jason at gcc dot gnu dot org  2009-04-05 19:33 -------
*** Bug 39642 has been marked as a duplicate of this bug. ***


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |piotr dot wyderski at gmail
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jack dot q dot word at gmail dot com]

------- Comment #8 from jack dot q dot word at gmail dot com  2009-08-13 05:01 -------
Created an attachment (id=18348)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18348&action=view)
tuple & union examples with possibly proper variadic return type case relying
on variadic template expansion


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jack dot q dot word at gmail dot com]

------- Comment #9 from jack dot q dot word at gmail dot com  2009-08-13 05:04 -------
(In reply to comment #8)
> Created an attachment (id=18348)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18348&action=view) [edit]
> tuple & union examples with possibly proper variadic return type case relying
> on variadic template expansion
> 

the unnamed structs/unions, and RecursiveStruct/Union can be discarded, and use
'byte Data[VarTypeNav< cT, vT...>::Size];' ...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jack dot q dot word at gmail dot com]

------- Comment #10 from jack dot q dot word at gmail dot com  2009-08-13 05:05 -------

> 'byte Data[VarTypeNav< cT, vT...>::Size];' ...

or 'char Data[VarTypeNav< cT, vT...>::Size];' ...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[jack dot q dot word at gmail dot com]

------- Comment #11 from jack dot q dot word at gmail dot com  2009-08-13 05:14 -------
(From update of attachment 18348)
template< class cT, class... vT >
struct VarTypeNav
{
        typedef cT T;
        typedef VarTypeNav< vT..., void > Next;
        struct scT { cT v; };
        static const size_t Size =
                sizeof(scT) + Next::Size;
        static const size_t Count =
                1 + Next::Count;
};

template< class... vT >
struct VarTypeNav< void, vT... >
{
        typedef void T; 
        typedef void Next;
        static const size_t Size = 0;
        static const size_t Count = 0;
};

template< const size_t nIndex, class cT, class... vT >
struct VarTypeSelect
{
        typedef VarTypeSelect< nIndex-1, vT... >::T T;
        struct scT { T v; };
        static const size_t Offset =
                sizeof(scT) + VarTypeSelect< nIndex-1, vT... >::Offset;
};

template< class cT, class... vT >
struct VarTypeSelect< 0, cT, vT... >
{
        typedef cT T;
        static const size_t Offset = 0;
};

template< class cT, class... vT >
struct Tuple
{
        char Data[VarTypeNav<cT,vT...>::Size];
        template< const size_t index >
        VarTypeSelect< index, vT... >::T & operator [] ( const size_t index )
        {
                static_assert(!(index > VarTypeNav< vT... >::Count ), "Index
out of bounds");
                char * pThisChars = (char *) this;
                return *(
                        (VarTypeSelect< index, vT... >::T *)
                                pThisChars[ VarTypeSelect< index, vT...
>::Offset ]));
        }
        template< const size_t index >
        const VarTypeSelect< index, vT... >::T & operator [] ( const size_t
index ) const
        {
                static_assert(!(index > VarTypeNav< vT... >::Count ), "Index
out of bounds");
                const char * pThisChars = (const char *) this;
                return *(
                        (const VarTypeSelect< index, vT... >::T *)
                                pThisChars[ VarTypeSelect< index, vT...
>::Offset ]));
        }
};

int main() {
        Tuple< size_t, char * > x; /* = { 32, new char[32] }; *//* ? */
        x[0] = 32;
        x[1] = new char[32];
        x[1][31] = 0;
        return (int) &x[1][0] != 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722

[Bug c++/35722] [C++0x] Variadic templates expansion into non-variadic class template

[chris at bubblescope dot net]

------- Comment #12 from chris at bubblescope dot net  2010-01-22 09:11 -------
Just for anyone who comes to this bug, it can be worked around by doing
something like:

template<template <typename...> T, typename... Args>
struct Join
{ typedef T<Args...> type; }

Although of course that isn't a fix (and unfortunately a fix is beyond me).


-- 

chris at bubblescope dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |chris at bubblescope dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722