[Bug c++/46394] New: [C++0X] no matching function with default template argument

Discussion:

marc.glisse at normalesup dot org

15 years ago

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

Summary: [C++0X] no matching function with default template
argument
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: ***@gcc.gnu.org
ReportedBy: ***@normalesup.org

This code recently stopped compiling. (I have a remove_cv on top of the
remove_reference in the original code but it didn't look necessary to reproduce
the problem)

#include <utility>
#include <tuple>
#include <type_traits>
struct A {
template<class...U,class=
typename std::enable_if<
!std::is_same<
std::tuple<typename std::remove_reference<U>::type...>,
std::tuple<A>

::value
::type

A(U&&...u) ;
};
int main(){
A a(1,2,3);
}

bug.cc: In function ‘int main()’:
bug.cc:16:11: error: no matching function for call to ‘A::A(int, int, int)’
bug.cc:13:13: note: candidates are: template<class ... U, class> A::A(U&& ...)
bug.cc:4:8: note: constexpr A::A(const A&)
bug.cc:4:8: note: constexpr A::A(A&&)

paolo.carlini at oracle dot com

15 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

Paolo Carlini <paolo.carlini at oracle dot com> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2010.11.09 14:58:23
CC| |jason at gcc dot gnu.org
Summary|[C++0X] no matching |[C++0X] [4.6 Regression] no
|function with default |matching function with
|template parameter |default template parameter
Ever Confirmed|0 |1

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2010-11-09 14:58:23 UTC ---
Let's add Jason. I'm pretty sure this isn't a library issue because the same
happens with just:

template<class...U>
struct tuple;

and outside std::tuple the rest is pretty trivial as far as the library is
concerned.

paolo.carlini at oracle dot com

15 years ago

Permalink

marc.glisse at normalesup dot org

14 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

--- Comment #2 from Marc Glisse <marc.glisse at normalesup dot org> 2010-12-17 20:04:18 UTC ---
Note that if I change the function to:

template<class...U,class=
typename std::enable_if<
!std::is_same<
std::tuple<U&&...>,
void

::value
::type

A(U&&...u) ;

I get:

sorry, unimplemented: use of 'type_pack_expansion' in template

hjl.tools at gmail dot com

14 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

H.J. Lu <hjl.tools at gmail dot com> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |dseketel at redhat dot com

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> 2010-12-17 20:10:12 UTC ---
It is caused by revision 166179:

http://gcc.gnu.org/ml/gcc-cvs/2010-11/msg00065.html

dodji at gcc dot gnu.org

14 years ago

Permalink

dodji at gcc dot gnu.org

14 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

--- Comment #4 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-01-04 15:32:53 UTC ---
I think what's happening is, at some point during template parameters
fixup (to build proper canonical types for dependent parms) we try to
substitute the U template parameter pack [and the the remaining unamed
template parm] into the pattern of the default argument
std::remote_reference<U>::type... . The TYPENAME_TYPE case of tsubst then
logically calls tsubst_aggr_type on 'std::remote_reference<U>'. That
later function in turn calls lookup_template_class with
std::remote_reference as argument to D1 and a TYPE_PACK_EXPANSION
built for the template parameter U (by template_parm_to_arg) and
argument to ARGLIST.

At that point we are trying to match a template argument which is
a pack expansion with a template parameter that is not a
parameter pack - and we hit
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722.

So I think I am going to focus on that bug and see.

dodji at gcc dot gnu.org

14 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

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

What |Removed |Added
----------------------------------------------------------------------------
Depends on|35722 |

--- Comment #5 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-02-04 19:53:24 UTC ---
Actually my previous analysis wasn't quite right. Rather, the
substitution of the fixed up U into std::remove_reference<U>::type...,
fails. It fails because we fail to compare the fixed up U with the
non-fixed up U. And after that the sky falls.

So this has nothing to do with
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35722, luckily. Pheew.

A candidate patch was sent to to
http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00295.html along with a
smaller reproducer.

rguenth at gcc dot gnu.org

14 years ago

Permalink

dodji at gcc dot gnu.org

14 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

--- Comment #6 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-02-20 17:37:06 UTC ---
Author: dodji
Date: Sun Feb 20 17:37:03 2011
New Revision: 170341

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=170341
Log:
PR c++/46394

gcc/cp/

PR c++/46394
* pt.c (tsubst_pack_expansion): do not use
cp_tree_equal/same_type_p to detect an expansion of a parameter
pack.

gcc/testsuite/

PR c++/46394
* g++.dg/template/typedef38.C: New test.

Added:
trunk/gcc/testsuite/g++.dg/template/typedef38.C
Modified:
trunk/gcc/cp/ChangeLog
trunk/gcc/cp/pt.c
trunk/gcc/testsuite/ChangeLog

dodji at gcc dot gnu.org

14 years ago

Permalink

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46394

--- Comment #7 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-02-20 18:08:14 UTC ---
Fixed in trunk (4.6).

dodji at gcc dot gnu.org

14 years ago

Permalink