[Bug c++/53856] New: Default argument allowed on member defined outside of class template

[Bug c++/53856] New: Default argument allowed on member defined outside of class template

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53856

             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 = int>
struct A<T>::B
{
    int i;
};

int main()
{
    A<int>::B b = { };
    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’s 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 specified
on
          the declaration of a member of a class template outside of its class
  template<typename T = int>
                    ^

As does Clang++

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

Solaris CC accepts it.

[Bug c++/53856] Default argument allowed on member defined outside of class template

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53856

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
      Known to fail|                            |3.4.3, 4.1.2, 4.6.3, 4.8.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-07-04 16:43:53 UTC ---
Modifying the example to use a member template of a non-template, which I
believe *is* valid, gets rejected:

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

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

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

bug.cc:8:11: error: default argument for template parameter for class enclosing
'struct A::B<T>'

This seems to be completely backwards, the invalid case is accepted and the
valid case rejected!

Comeau online rejects it for the same reason as the code in commnt 0 above:

"ComeauTest.c", line 6: error: a default template argument cannot be specified
on
          the declaration of a member of a class template outside of its class
  template<typename T = int>
                    ^

The wording is much better than G++'s, but I think the error is wrong, as it
talks about a member of a class template, whereas the code above is a member
template of a class. Not the same thing.

Clang++ and Solaris CC accept the modified version.

[Bug c++/53856] Default argument allowed on member defined outside of class template

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53856

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-09-22
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com
   Target Milestone|---                         |6.0
     Ever confirmed|0                           |1

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Looks like the first testcase is already fixed in 5. I'm looking into the
second one.

[Bug c++/53856] Default argument allowed on member defined outside of class template

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53856

--- Comment #3 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Mon Oct  5 21:43:26 2015
New Revision: 228501

URL: https://gcc.gnu.org/viewcvs?rev=228501&root=gcc&view=rev
Log:
/cp
2015-10-05  Paolo Carlini  <paolo.carlini@oracle.com>

        PR c++/53856
        * pt.c (check_default_tmpl_args): Per [temp.param]/9, do not
        reject default template arguments in out of class definitions
        of members of non-template classes.

/testsuite
2015-10-05  Paolo Carlini  <paolo.carlini@oracle.com>

        PR c++/53856
        * g++.dg/template/defarg19.C: New.
        * g++.dg/template/defarg20.C: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/template/defarg19.C
    trunk/gcc/testsuite/g++.dg/template/defarg20.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/53856] Default argument allowed on member defined outside of class template

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53856

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
           Assignee|paolo.carlini at oracle dot com    |unassigned at gcc dot gnu.org

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 6.0.