This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 119a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-12-20
[Moved to DR at the April, 2013 meeting.]
Consider an example like
template <int B, typename Type1, typename... Types> struct A; template<typename... Types> struct A<0, Types...> { }; A<0,int,int> t;In this case, the partial specialization seems well-formed by therules in 13.7.6 [temp.spec.partial], but it is not more specializedthan the primary template. However, 13.7.6.2 [temp.spec.partial.match]says that if exactly one matching specialization is found, it is used,which suggests that the testcase is well-formed. That seemsundesirable; I think a partial specialization that is not morespecialized than the primary template should be ill-formed.
If the example is rewritten so that both versions are partialspecializations, i.e.,
template <int B, typename... Types> struct A; template <int B, typename Type1, typename... Types> struct A<B, Type1, Types...> { } template<typename... Types> struct A<0, Types...> { }; A<0,int,int> t;There is implementation variance, with gcc and clang reporting anambiguity and EDG choosing the second specialization.
Proposed resolution (October, 2012):
Add the following as a new bullet in 13.7.6.1 [temp.spec.partial.general] paragraph 9:
...
The argument list of the specialization shall not be identical to theimplicit argument list of the primary template.
The specialization shall be more specialized than the primarytemplate (13.7.6.3 [temp.spec.partial.order]).
...