[Bug c++/57919] New: [C++11] Alias templates cause partial specialization to erroneously fail

[Bug c++/57919] New: [C++11] Alias templates cause partial specialization to erroneously fail

[cheesear at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57919

            Bug ID: 57919
           Summary: [C++11] Alias templates cause partial specialization
                    to erroneously fail
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cheesear at gmail dot com

Created attachment 30516
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30516&action=edit
MWE that causes the aforementioned error.

The use of alias templates can cause the compiler to think that a valid
template class instantiation is ambiguous. The file attached contains an
example that, when compiled with g++ (version 4.8.1_1 from Macports), results
in the following error:

$ g++ -std=c++11 er.cpp
er.cpp: In function 'int main()':
er.cpp:39:41: error: ambiguous class template instantiation for 'struct foo<1,
1, sequence<> >'
  using t = typename foo<1, 1, extents<>>::type;
                                         ^
er.cpp:26:8: error: candidates are: struct foo<A, B, sequence<integer<Ts>...> >
 struct foo<A, B, extents<Ts...>>
        ^
er.cpp:32:8: error:                 struct foo<B, B, sequence<integer<Ts>...> >
 struct foo<B, B, extents<Ts...>>
        ^
er.cpp:39:43: error: 'type' in 'struct foo<1, 1, sequence<> >' does not name a
type
  using t = typename foo<1, 1, extents<>>::type;
                                           ^

[Bug c++/57919] [C++11] Alias templates cause partial specialization to erroneously fail

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57919

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-11-23
     Ever confirmed|0                           |1

[Bug c++/57919] [C++11] Alias templates cause partial specialization to erroneously fail

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57919

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
MSVC also rejects this code for the same reason as GCC:
<source>(32): error C2752: 'foo<1,1,sequence<>>': more than one partial
specialization matches the template argument list
<source>(19): note: could be 'foo<A,B,sequence<integer<Ts>...>>'
<source>(25): note: or       'foo<B,B,sequence<integer<Ts>...>>'
<source>(32): error C2027: use of undefined type 'foo<1,1,sequence<>>'
<source>(32): note: see declaration of 'foo<1,1,sequence<>>'
<source>(32): error C2061: syntax error: identifier 'type'