[Bug c++/57765] New: [C++11] Variadic Template Specialization does not follow the INCITS/ISO​/IEC 14882-2011 standard

[aaronngray.lists at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57765

Bug ID: 57765
   Summary: [C++11] Variadic Template Specialization does not
follow the INCITS/ISO​/IEC 14882-2011 standard
   Product: gcc
   Version: 4.8.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: aaronngray.lists at gmail dot com

Prompted by a Stack Overflow article :-


http://stackoverflow.com/questions/17332749/vs2013-fails-with-variadic-template-specialization/

 There seems to be anomalies between GCC 4.8.1's 0x11 implementation
 and the standard.

 It shows the code :-

 template  struct OpF;

 template  struct
 OpF { };

 int foo(int x) { return 0; }

 OpF f;


 Given the C++ Standard outlaws this code, see 14.1 paragraphs 11 and 15.

 Note that GCC accepts the following code with either -std=gnu++11 or
 -std=c++11, the latter should be strict to the standard. Also given
 these paragraphs were in the draft C++ standard too.

 On the other hand GCC 4.8.1 will not accept a simple trailing 'int'
 parameter after a variadic template list.

  template < typename TR, typename ... Ts, int i> TR tester(Ts...);
 // error: parameter pack ‘Ts’ must be at the end of the template
 parameter list

 There seems to be quite an inconsistency even in an augmentation to
 the standard.

 On a personal note both these forms are syntactically correct but not
 semantically by the standard, given that this is just a simple type
 based pattern matching problem as far as I can see it would be nice to
 have it within the language as it seems to fit naturally with
 requirements.

[Bug c++/57765] [C++11] Variadic Template Specialization does not follow the INCITS/ISO​/IEC 14882-2011 standard

[aaronngray.lists at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57765

--- Comment #2 from AaronNGray  ---
Interesting ...from the standard, not in braces :-
"A template parameter pack of a function template shall not be followed by
another template parameter unless that template parameter can be deduced or has
a default argument"

The two paragraphs in full :-

14.1 [11] If a template-parameter of a class template or alias template has a
default template-argument, each subsequent template-parameter shall either have
a default template-argument supplied or be a template parameter pack. If a
template-parameter of a primary class template or alias template is a template
parameter pack, it shall be the last template-parameter. A template parameter
pack of a function template shall not be followed by another template parameter
unless that template parameter can be deduced or has a default argument
(14.8.2).

14.1 [15] If a template-parameter is a type-parameter with an ellipsis prior to
its optional identifier or is a parameter-declaration that declares a parameter
pack (8.3.5), then the template-parameter is a template parameter pack
(14.5.3). A template parameter pack that is a parameter-declaration whose type
contains one or more unexpanded parameter packs is a pack expansion. Similarly,
a template parameter pack that is a type-parameter with a
template-parameter-list containing one or more unexpanded parameter packs is a
pack expansion. A template parameter pack that is a pack expansion shall not
expand a parameter pack declared in the same template-parameter-list.

[Bug c++/57765] [C++11] Variadic Template Specialization does not follow the INCITS/ISO​/IEC 14882-2011 standard

[aaronngray.lists at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57765

AaronNGray  changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |INVALID

--- Comment #4 from AaronNGray  ---
If a template-parameter of a primary class template or alias template is a
template parameter pack, it shall be the last template-parameter.

template  struct
 OpF { };