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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/53856] New: Default argument allowed on member defined outside of class template
Date: Wed, 04 Jul 2012 16:39:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D53856

             Bug #: 53856
           Summary: Default argument allowed on member defined outside of
                    class template
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: redi@gcc.gnu.org


template<typename T>
struct A
{
    struct B;
};

template<typename T =3D int>
struct A<T>::B
{
    int i;
};

int main()
{
    A<int>::B b =3D { };
    return b.i;
}

This should be rejected according to [temp.param]/9

"A default template-argument shall not be specified in the
template-parameter-lists of the definition of a member of a class template =
that
appears outside of the member=E2=80=99s class."

All versions of G++ since at least 3.4 accept the code above.

Comeau online rejects it:

"ComeauTest.c", line 7: error: a default template argument cannot be specif=
ied
on
          the declaration of a member of a class template outside of its cl=
ass
  template<typename T =3D int>
                    ^

As does Clang++

bug2.cc:7:19: error: cannot add a default template argument to the definiti=
on
of a member of a class template
template<typename T =3D int>
                  ^   ~~~

Solaris CC accepts it.