[Bug c++/61953] New: [C++11] The template parameter pack of a function template should be the last template parameter

[Bug c++/61953] New: [C++11] The template parameter pack of a function template should be the last template parameter

[kariya_mitsuru at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61953

            Bug ID: 61953
           Summary: [C++11] The template parameter pack of a function
                    template should be the last template parameter
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kariya_mitsuru at hotmail dot com

The both sample codes below should cause compilation error but they are
compiled successfully by gcc.

==============================================
template<class... T, class... U> void f() { }
==============================================

===========================================
template<class... T, class U> void g() { }
===========================================

According to C++11 standard 14.1 Template parameters [temp.param] paragraph 11,
"A template parameter pack of a function template shall not be followed by
another template parameter unless that template parameter can be deduced from
the parameter-type-list of the function template or has a default argument."

The latest draft is more clarified using the following example.

=======================================================================
// U can be neither deduced from the parameter-type-list nor specified
template<class... T, class... U> void f() { } // error
template<class... T, class U> void g() { } // error
=======================================================================

cf. http://melpon.org/wandbox/permlink/zO14UQDvxpXwRfYm

[Bug c++/61953] [C++11] The template parameter pack of a function template should be the last template parameter

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61953

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-12-14
     Ever confirmed|0                           |1

[Bug c++/61953] [C++11] The template parameter pack of a function template should be the last template parameter

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61953

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid
                 CC|                            |ville.voutilainen at gmail dot com
      Known to fail|                            |4.8.2, 4.9.1, 5.0

--- Comment #1 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Clang also silently accepts the code.

[Bug c++/61953] [C++11] The template parameter pack of a function template should be the last template parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61953

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Clang and GCC both accept the code slightly.
ICC accepts the code with a warning:
<source>(1): warning #2922: template parameter "U" cannot be used because it
follows a parameter pack and cannot be deduced from the parameters of function
template "f"
  template<class... T, class... U> void f() { }
                                ^

<source>(2): warning #2922: template parameter "U" cannot be used because it
follows a parameter pack and cannot be deduced from the parameters of function
template "g"
  template<class... T, class U> void g() { }
                             ^


MSVC rejects the code:
<source>(1): error C3547: template parameter 'U' cannot be used because it
follows a template parameter pack and cannot be deduced from the function
parameters of 'f'
<source>(1): note: see declaration of 'U'
<source>(2): error C3547: template parameter 'U' cannot be used because it
follows a template parameter pack and cannot be deduced from the function
parameters of 'g'
<source>(2): note: see declaration of 'U'

[Bug c++/61953] [C++11] The template parameter pack of a function template should be the last template parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61953

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 69623.

*** This bug has been marked as a duplicate of bug 69623 ***