public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "davveston at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/99699] New: Type deduction failure for deducing a non-type template parameter via another deducible structural type (class template specialization) non-type template parameter Date: Sun, 21 Mar 2021 18:14:32 +0000 [thread overview] Message-ID: <bug-99699-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99699 Bug ID: 99699 Summary: Type deduction failure for deducing a non-type template parameter via another deducible structural type (class template specialization) non-type template parameter Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: davveston at gmail dot com Target Milestone: --- The following program: // -------------------------------------------- template<int N> struct S {}; template<S s> struct U {}; template<typename> struct V { V() = delete; }; template <int N, S<N> s> struct V<U<s>> {}; V<U<S<0>{}>> v{}; // #1 // Expected: use partial specialization #1 // GCC actual: error (rejects-valid): use of deleted function int main() {} // -------------------------------------------- is rejected by gcc HEAD 11.0.1 20210320 (experimental) when compiling with 'g++ prog.cc -Wall -Wextra -std=c++2b', as #1 matches to the primary template instead of the partial specialization. It seems to find the non-type template parameter N non-deducible; however all arguments of the partial specialization are arguably deducible from the 'U<S<0>{}>' argument to the primary template: - 'A' / 'P' matching 'U<S<0>{}>' / 'U<s>' deduces 's' to 'S<0>{}' and its type to 'S<0>', - 'A' / 'P' matching 'S<0>' to 'S<N>' deduces 'N' to '0'; 'N' is particularly not in a non-deduced context above, as it's not used in sub-expression in the non-type template parameter 's' of the partial specialization. Demo: https://wandbox.org/permlink/QQQxa3BhBTMM476E
next reply other threads:[~2021-03-21 18:14 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-21 18:14 davveston at gmail dot com [this message] 2022-04-07 9:30 ` [Bug c++/99699] " davveston at gmail dot com 2022-06-02 18:06 ` ppalka at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-99699-4@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).