[Bug c++/48322] New: [C++0x] Plural parameter packs are not expanded well

[Bug c++/48322] New: [C++0x] Plural parameter packs are not expanded well

[gintensubaru at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48322

           Summary: [C++0x] Plural parameter packs are not expanded well
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gintensubaru@gmail.com


Source Code (bug.cc):


#include <typeinfo>
#include <cxxabi.h>
#include <cstdlib>
#include <iostream>

template<class T>
void print_typename()
{
  int status = 0;
  char* const name = abi::__cxa_demangle( typeid(T).name(), 0, 0, &status );
  std::cout << name << std::endl;
  std::free( name );
}

#include <type_traits>
#include <utility>
#include <tuple>

template<class... Ts>
struct X
{
  template< class... Us,
    class Tuple = std::tuple<
      std::pair<Ts, Us>...
    >
  >
  static void test( Us... ) {
    print_typename<Tuple>();
  }

};

int main()
{
                     // expected
  X<>::test();       // std::tuple<>
  X<int>::test(1);   // std::tuple<std::pair<int, int>>
  X<int>::test(1.0); // std::tuple<std::pair<int, double>>

  X<>::test(1);      // no matching function
  X<int>::test();    // no matching function
}



Output:

std::tuple<>
std::tuple<std::pair<int, int> >
std::tuple<std::pair<double, double> >
std::tuple<std::pair<int, int> >
std::tuple<>

[Bug c++/48322] [C++0x] Plural parameter packs are not expanded well

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48322

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.05.25 04:24:42
                 CC|                            |jason at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-25 04:24:42 UTC ---
Reduced, compile-time testcase:

template <class... T> struct tuple;
template <class T> struct tuple<T> { T t; };

template <class T, class U> struct pair;
template<> struct pair<int,double> { };

template <class... Ts>
struct A
{
  template <class... Us,
            class V = tuple<pair<Ts,Us>...> >
  static void f()
  {
    V v;
  }
};

int main()
{
  A<int>::f<double>();
}

The problem is that partial instantiation doesn't replace Ts with {int}, but it
does lower the level of Us, so by the time we get to deduction Ts and Us both
have level 1 and so both are replaced with {double}.  This will be complicated
to fix.

[Bug c++/48322] [C++0x] Plural variadic parameter packs are not expanded well

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48322

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo.carlini at oracle dot
                   |                            |com

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-15 18:01:56 UTC ---
*** Bug 49225 has been marked as a duplicate of this bug. ***

[Bug c++/48322] [C++0x] Plural variadic parameter packs are not expanded well

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48322

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> 2011-11-21 02:04:59 UTC ---
Author: jason
Date: Mon Nov 21 02:04:54 2011
New Revision: 181547

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=181547
Log:
    PR c++/48322
gcc/cp/
    * cp-tree.h (PACK_EXPANSION_EXTRA_ARGS): New.
    * cp-tree.def (EXPR_PACK_EXPANSION): Add an operand for it.
    * pt.c (tsubst_pack_expansion): Set and use it.
    (iterative_hash_template_arg): Hash it.
    (template_args_equal): Compare it.
    (comp_template_args_with_info): Handle nulls.
    * tree.c (cp_walk_subtrees): Walk it.
    * typeck.c (structural_comptypes): Compare it.
    * ptree.c (cxx_print_type): Print it.
libstdc++-v3/
    * include/std/tuple (tuple(_UElements&&...)): Fix SFINAE.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/variadic120.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.def
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/ptree.c
    trunk/gcc/cp/tree.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/cpp0x/sfinae26.C
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/std/tuple

[Bug c++/48322] [C++0x] Plural variadic parameter packs are not expanded well

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48322

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.0

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> 2011-11-21 02:18:34 UTC ---
Fixed for 4.7.