220 9826 article Path: news.gmane.org!not-for-mail From: Johannes Schaub Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: auto variable templates? 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>> >> >> >> template constexpr auto X = 42; >> >> >> >> int main() >> >> { >> >> static_assert(X == 42, ""); >> >> } >> >> >> >> >> >> [dcl.spec.auto]/4 says that auto is allowed when declaring variables in >> >> namespace-scope, but doesn't explicitly say in variable templates - >> >> consequently this is ill-formed. >> > >> > >> > A specialization of a variable template is a variable, so this is >> > allowed. >> > >> >> I don't understand this reason. The following is not a specialization >> of a variable template, is it? >> >> template constexpr auto X = 42; >> >> The Standard says in 7.1.6.4p6, "A program that uses auto or >> decltype(auto) in a context not explicitly allowed in this section is >> ill-formed." >> >> The section does not explicitly allow "auto" for variable templates. >> Why does it matter that the specialization of that template is a >> variable? > > > Because the validity of a template isn't governed by the usual language > rules. 14.6/8: "No diagnostic shall be issued for a template for which a > valid specialization can be generated." > It's also not clear to me where to draw the line. Consider class Y { typedef int type; }; template struct X { }; The specialization of this template does not have template parameters, since it's a normal class. A diangostic should therefor not be generated for the class template, since the specialization is valid. However, clang complains "main.cpp:5:13: error: 'type' is a private member of 'Y'" -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. .