[Bug c++/35989] New: code rejected in template specialization (4.2 did accept)

[Bug c++/35989] New: code rejected in template specialization (4.2 did accept)

[debian-gcc at lists dot debian dot org]

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[forwarded from http://bugs.debian.org/470850]

code is rejected by 4.3.1 20080420, accepted by 4.2.3

  The following code has three specializations of a template.
The third one compiles with g++-4.2 but gives an error with g++-4.3 :

vdanjean@cayuga:/tmp/toto$ g++-4.3 -Wall -c test.cpp 
test.cpp:30: error: template parameters not used in partial specialization:
test.cpp:30: error:         ‘T’
test.cpp:30: error:         ‘A’
vdanjean@cayuga:/tmp/toto$

It seems to me that my code is correct and g++-4.3 wrong: I really use T
and A in the partial specialization.


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           Summary: code rejected in template specialization (4.2 did
                    accept)
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989

[Bug c++/35989] code rejected in template specialization (4.2 did accept)

[debian-gcc at lists dot debian dot org]

------- Comment #1 from debian-gcc at lists dot debian dot org  2008-04-20 16:36 -------
Created an attachment (id=15500)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15500&action=view)
test case


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989

[Bug c++/35989] code rejected in template specialization (4.2 did accept)

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-04-20 17:31 -------
EDG agrees with gcc:

/tmp/test.cpp(29): warning #885: template parameter "T" is not used in or
cannot be deduced from the template argument list of class template
"remote_trait<std::vector<_Tp, _Alloc>::iterator>"
  template<class T, class A>
                 ^

/tmp/test.cpp(29): warning #885: template parameter "A" is not used in or
cannot be deduced from the template argument list of class template
"remote_trait<std::vector<_Tp, _Alloc>::iterator>"
  template<class T, class A>
                          ^

which means that from an std::vector<T, A>::iterator type T and A cannot
be deduced.  Which in the end means that this specialization is never
going to be selected.  Whether this is rightfully diagnosed as error by
gcc I don't know.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989

[Bug c++/35989] code rejected in template specialization (4.2 did accept)

[da_cra_hunt at yahoo dot com]

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------- Comment #3 from da_cra_hunt at yahoo dot com  2009-07-23 17:34 -------
Simple case :


template<typename C> struct A {};
template<typename C> struct B { struct Inner {}; };

template<typename K>
struct A<typename B<K>::Inner> {};


4.1.2/VS2005 compile quietly. 4.3.2 (g++ -c test.cpp) gives :

kk.cpp:5: error: template parameters not used in partial specialization:
kk.cpp:5: error:         ‘K’


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da_cra_hunt at yahoo dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |da_cra_hunt at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989

[Bug c++/35989] code rejected in template specialization (4.2 did accept)

[jwakely dot gcc at gmail dot com]

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------- Comment #4 from jwakely dot gcc at gmail dot com  2009-07-24 10:12 -------
(In reply to comment #3)
> Simple case :
> 
> 
> template<typename C> struct A {};
> template<typename C> struct B { struct Inner {}; };
> 
> template<typename K>
> struct A<typename B<K>::Inner> {};
> 
> 
> 4.1.2/VS2005 compile quietly. 4.3.2 (g++ -c test.cpp) gives :
> 
> kk.cpp:5: error: template parameters not used in partial specialization:
> kk.cpp:5: error:         ‘K’
> 

I think this is invalid because K is used in a non-deduced context


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989

[Bug c++/35989] code rejected in template specialization (4.2 did accept)

[jwakely dot gcc at gmail dot com]

------- Comment #5 from jwakely dot gcc at gmail dot com  2009-07-24 10:29 -------
(In reply to comment #4)
> I think this is invalid because K is used in a non-deduced context

Which is the same problem as with the original testcase - this is not a bug in
gcc.

According to 14.5.4.1 [temp.class.spec.match] paragraph 2 the template
arguments of the partial specialisation must be deduced, but in the testcases
they appear in non-deduced contexts as defined by 14.8.2.4 [temp.deduct]
paragraph 4.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989

[Bug c++/35989] code rejected in template specialization (4.2 did accept)

[paolo dot carlini at oracle dot com]

------- Comment #6 from paolo dot carlini at oracle dot com  2009-07-24 10:42 -------
Closing...


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paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35989