Re: c++/7033: [3.3/3.4 regression] [2003-05-30] Partial template specializations accepted even if a template parameter is used in a non-deduced context

["Giovanni Bajo" <giovannibajo at libero dot it>]

The following reply was made to PR c++/7033; it has been noted by GNATS.

From: "Giovanni Bajo" <giovannibajo@libero.it>
To: <gcc-gnats@gcc.gnu.org>,
	<Theodore.Papadopoulo@sophia.inria.fr>,
	<gcc-bugs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>,
	<Lionel.Champalaune@sophia.inria.fr>
Cc:  
Subject: Re: c++/7033: [3.3/3.4 regression] [2003-05-30] Partial template specializations accepted even if a template parameter is used in a non-deduced context
Date: Mon, 5 May 2003 13:20:01 +0200

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7033
 
 The specialization should not be selected because §14.8.2.4p4 clearly
 specifies that A<T>::B<Q> is a non-deduced context for both T and Q.
 
 But there's more: 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:
 
 -----------------------------------------------
 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'
 
 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> > {};
 -----------------------------------------------
 
 which is currently accepted by 3.3 and 3.4, even if "V" is used only in
 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'
 
 (actually, the error message could be "template parameter used in
 non-decuded context", but anyway).
 
 This is a reject-legal regression, and I now flagged it as such.
 
 Giovanni Bajo