[Bug c++/56152] New: explicit template instantiation of protected template function redeclared as public fails

[Bug c++/56152] New: explicit template instantiation of protected template function redeclared as public fails

[froydnj at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56152

             Bug #: 56152
           Summary: explicit template instantiation of protected template
                    function redeclared as public fails
    Classification: Unclassified
           Product: gcc
           Version: 4.4.7
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: froydnj@gcc.gnu.org


Compiling the following testcase:

enum Flavor {
  A,
  B
};

template<enum Flavor F>
class C
{
protected:
  template<typename T>
  static T f(T x)
  {
    if (F == A)
      return x;
    else
      return ~x;
  }
};

class AC : public C<A>
{
private:
  typedef C<A> super;

public:
  using super::f;
};

unsigned int
explicit_variable(unsigned int x)
{
  unsigned int (*func)(unsigned int) = AC::f<unsigned int>;

  return func(x);
}

unsigned int
explicit_call_instantiation(unsigned int x)
{
  return AC::f<unsigned int>(x);
}

unsigned int
implicit_call_instantiation(unsigned int x)
{
  return AC::f(x);
}

produces:

template-instantiation-bug.cpp: In function ‘unsigned int
explicit_variable(unsigned int)’:
template-instantiation-bug.cpp:11:12: error: ‘static T C<F>::f(T) [with T =
unsigned int, Flavor F = (Flavor)0u]’ is protected
template-instantiation-bug.cpp:32:44: error: within this context
template-instantiation-bug.cpp:11:12: error: ‘static T C<F>::f(T) [with T =
unsigned int, Flavor F = (Flavor)0u]’ is protected
template-instantiation-bug.cpp:32:44: error: within this context
template-instantiation-bug.cpp:11:12: error: ‘static T C<F>::f(T) [with T =
unsigned int, Flavor F = (Flavor)0u]’ is protected
template-instantiation-bug.cpp:32:44: error: within this context

It is not obvious to me that this is the right answer, given that both
explicit_call_instantiation and implicit_call_instantiation work.

All versions of GCC that I've tested reject the testcase (4.4 - 4.8).  Clang
(2.8 - 3.2) accepts the testcase.  MSVC version 9 rejects it.  My MSVC version
10 installation appears to be busted, or I'd test it there too.

[Bug c++/56152] explicit template instantiation of protected template function redeclared as public fails

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56152

Daniel Krügler <daniel.kruegler at googlemail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |daniel.kruegler at
                   |                            |googlemail dot com

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-01-30 20:24:06 UTC ---
GCC 4.8.0 trunk behaves similar. I think the situation is currently not clear
by the language. It looks like a manifestation of

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1551

to me. Especially bullet 3 in the P/R looks relevant to me.

[Bug c++/56152] explicit template instantiation of protected template function redeclared as public fails

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56152

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-08-21
     Ever confirmed|0                           |1

[Bug c++/56152] explicit template instantiation of protected template function redeclared as public fails

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56152

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2013-08-21 00:00:00         |2021-12-11
           Keywords|                            |rejects-valid

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
class C
{
protected:
  template<typename T>
  static T f(T x){return x;}
};

struct AC : C
{
  using C::f;
};

unsigned int (*func)(unsigned int) = AC::f;