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From: "rs2740 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/100708] New: dynamic_cast can convert xvalue to lvalue
Date: Thu, 20 May 2021 20:18:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100708

            Bug ID: 100708
           Summary: dynamic_cast can convert xvalue to lvalue
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com
  Target Milestone: ---

GCC accepts

struct A { virtual ~A() {}; };
struct B : A {} b;

void g ()
{
    dynamic_cast<B&>(static_cast<A&&>(b));
}

[expr.dynamic.cast]/2 says that for dynamic_cast<T>(v):

If T is an lvalue reference type, v shall be an lvalue of a complete class
type, and the result is an lvalue of the type referred to by T.=