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From: "ville.voutilainen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/95915] New: std::variant doesn't like types with a
 defaulted virtual destructor
Date: Fri, 26 Jun 2020 14:40:53 +0000
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X-Bugzilla-Version: 11.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95915

            Bug ID: 95915
           Summary: std::variant doesn't like types with a defaulted
                    virtual destructor
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com
  Target Milestone: ---

>>From Patrice Roy:

The following code compiled in C++17 but seems broken in C++20, at least
according the Clang and gcc:

#include <variant>
struct X {
   virtual ~X() =3D default;
};
int main() {
   std::variant<X> v;
}

This is because variant's storage uses an _Uninitialized type that hacks
around a compiler bug, where the type X above wasn't literal. Now that it
is, the hack breaks. Since variant's other base-layers handle triviality
of special member functions properly, this hack can now be removed.=