[Bug c++/13640] [3.3/3.4 regression] Failing to reject class template partial specialization which can never be selected

["gdr at integrable-solutions dot net" <gcc-bugzilla@gcc.gnu.org>]

------- Additional Comments From gdr at integrable-solutions dot net  2004-01-10 23:25 -------
Subject: Re:  New: [3.3/3.4 regression] Failing to reject class template partial specialization which can never be selected

"giovannibajo at libero dot it" <gcc-bugzilla@gcc.gnu.org> writes:

| This is basically c++/7033, cleaned and simplified. Comment 6 (quoting myself):
| 
| ---------------------------------------------------------------------------
|  I'm confident that defining a partial template
|  specialization whose arguments can't be fully deduced from the arguments of
|  the original template is ill-formed. In fact, GCC correctly rejects this:

I disagree.  Declaring/defining a partial specialization that can
never be selected by partial ordering is not ill-formed.

|  -----------------------------------------------
|  template <class> struct K;
|  
|  template <class T>
|  struct K<int> {};
|  -----------------------------------------------
|  pr7033.cpp:4: error: template parameters not used in partial specialization:
|  pr7033.cpp:4: error:         `T'

That situation is different.  There is a note somewhere in the standard
saying that every template parameter shall be used in a partial
specialization.  However, that note does not imply that the resulting
partial specialization could ever be selected by partial ordering or
template argument deduction.

|  but it fails to reject this:
|  
|  -----------------------------------------------
|  template <typename, typename> struct S;
|  
|  template <template <typename> class C,
|  typename T,
|  typename V>
|  struct S<C<T>,typename C<T>::template it<V> > {};
|  -----------------------------------------------

I'm well aware of this example -- as I used it to discuss related
topics on the committee reflector.

|  which is currently accepted by 3.3 and 3.4, even if "V" is used only in

And that is allowed by the standard.

|  non-deduced contexts. This is a regression (rechecked on CVS 20050305 for
|  both 3.3 and 3.4) with respect to 2.95 which was rejecting the code:
|  
|  pr7033.cpp:6: template parameters not used in partial specialization:
|  pr7033.cpp:6:         `V'

That is a bogus behaviour.

|  (actually, the error message could be "template parameter used in
|  non-decuded context", but anyway).
|  
|  This is an accepts-invalid regression, and I now flagged it as such.

I disagree: it is not accepts-invalid.  

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13640