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* [Bug c++/105553] New: Deduction when attempting to create an array with an element type that is an abstract class @ 2022-05-10 18:36 glenjofe at gmail dot com 2022-05-11 7:38 ` [Bug c++/105553] [11/12/13 Regression] " rguenth at gcc dot gnu.org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: glenjofe at gmail dot com @ 2022-05-10 18:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105553 Bug ID: 105553 Summary: Deduction when attempting to create an array with an element type that is an abstract class Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: glenjofe at gmail dot com Target Milestone: --- Starting with GCC11, the following definition of a trait to check if a type is abstract no longer works in any standard mode: template<class T> class is_abstract { template<class U> static char (&check(U(*)[1]))[2]; template<class U> static char check(...); public: static const bool value = sizeof(check<T>(0)) == sizeof(char); }; struct abstract { virtual void function() = 0; }; static_assert(is_abstract<abstract>::value, "ok"); The static assertion trigger on GCC11 and above, even in older standard modes. It compiles fine on GCC10 and below. Various libraries in Boost use the above definition of is_abstract especially in C++03. The basis was the following wording in [temp.deduct] until C++17: "Type deduction may fail for the following reasons: - Attempting to create an array with an element type that is void, a function type, a reference type, or an abstract class type, or attempting to create an array with a size that is zero or negative." The "or an abstract class type" was absent in C++03, added by CWG337. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/105553] [11/12/13 Regression] Deduction when attempting to create an array with an element type that is an abstract class 2022-05-10 18:36 [Bug c++/105553] New: Deduction when attempting to create an array with an element type that is an abstract class glenjofe at gmail dot com @ 2022-05-11 7:38 ` rguenth at gcc dot gnu.org 2022-05-16 16:44 ` [Bug c++/105553] [11/12/13 Regression] [DR1640] " jason at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2022-05-11 7:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105553 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|Deduction when attempting |[11/12/13 Regression] |to create an array with an |Deduction when attempting |element type that is an |to create an array with an |abstract class |element type that is an | |abstract class Target Milestone|--- |11.4 Keywords| |rejects-valid ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/105553] [11/12/13 Regression] [DR1640] Deduction when attempting to create an array with an element type that is an abstract class 2022-05-10 18:36 [Bug c++/105553] New: Deduction when attempting to create an array with an element type that is an abstract class glenjofe at gmail dot com 2022-05-11 7:38 ` [Bug c++/105553] [11/12/13 Regression] " rguenth at gcc dot gnu.org @ 2022-05-16 16:44 ` jason at gcc dot gnu.org 2022-05-16 16:46 ` jason at gcc dot gnu.org 2022-05-16 21:14 ` glenjofe at gmail dot com 3 siblings, 0 replies; 5+ messages in thread From: jason at gcc dot gnu.org @ 2022-05-16 16:44 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105553 Jason Merrill <jason at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|[11/12/13 Regression] |[11/12/13 Regression] |Deduction when attempting |[DR1640] Deduction when |to create an array with an |attempting to create an |element type that is an |array with an element type |abstract class |that is an abstract class Resolution|--- |INVALID CC| |jason at gcc dot gnu.org Status|UNCONFIRMED |RESOLVED --- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> --- That wording was removed by wg21.link/p0929r2 to address wg21.link/cwg1640 , which is about this exact pattern. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/105553] [11/12/13 Regression] [DR1640] Deduction when attempting to create an array with an element type that is an abstract class 2022-05-10 18:36 [Bug c++/105553] New: Deduction when attempting to create an array with an element type that is an abstract class glenjofe at gmail dot com 2022-05-11 7:38 ` [Bug c++/105553] [11/12/13 Regression] " rguenth at gcc dot gnu.org 2022-05-16 16:44 ` [Bug c++/105553] [11/12/13 Regression] [DR1640] " jason at gcc dot gnu.org @ 2022-05-16 16:46 ` jason at gcc dot gnu.org 2022-05-16 21:14 ` glenjofe at gmail dot com 3 siblings, 0 replies; 5+ messages in thread From: jason at gcc dot gnu.org @ 2022-05-16 16:46 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105553 --- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> --- I implemented P0929R2 in r11-5036. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/105553] [11/12/13 Regression] [DR1640] Deduction when attempting to create an array with an element type that is an abstract class 2022-05-10 18:36 [Bug c++/105553] New: Deduction when attempting to create an array with an element type that is an abstract class glenjofe at gmail dot com ` (2 preceding siblings ...) 2022-05-16 16:46 ` jason at gcc dot gnu.org @ 2022-05-16 21:14 ` glenjofe at gmail dot com 3 siblings, 0 replies; 5+ messages in thread From: glenjofe at gmail dot com @ 2022-05-16 21:14 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105553 --- Comment #3 from Glen Joseph Fernandes <glenjofe at gmail dot com> --- I would have expected this to only take effect in C++20 standards mode, leaving C++03 through C++17 modes with no change in behavior. Given the following intention in your commit message: > This change was moved as a DR, so I'm applying it to all standard levels. This could be reconsidered if it causes problems, but I don't expect it to. I'm going to assume that in general this wasn't a problem for most users. :) ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-05-16 21:14 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-05-10 18:36 [Bug c++/105553] New: Deduction when attempting to create an array with an element type that is an abstract class glenjofe at gmail dot com 2022-05-11 7:38 ` [Bug c++/105553] [11/12/13 Regression] " rguenth at gcc dot gnu.org 2022-05-16 16:44 ` [Bug c++/105553] [11/12/13 Regression] [DR1640] " jason at gcc dot gnu.org 2022-05-16 16:46 ` jason at gcc dot gnu.org 2022-05-16 21:14 ` glenjofe at gmail dot com
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