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Date: Tue, 8 Jun 2021 12:45:39 +0100
From: Jonathan Wakely <jwakely@redhat.com>
To: paulkoning@comcast.net
Cc: gcc@gcc.gnu.org, Paul Smith <paul@mad-scientist.net>
Subject: Re: GCC 10.2: undefined reference to vtable: missing its key function
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(This should have been on the gcc-help list.)

> I may be remembering wrong, but -- doesn't dynamic_cast look for a vtable?

It uses a vtable if one is present, it can't cause one to be
introduced, so ...

>So if you do a dynamic cast mentioning that class you'd get such a reference.

No.

> Or is that an error when applied to a non-polymorphic class?

You can use dynamic_cast to upcast (i.e. from derived to base) for
non-polymorphic class types. It is an error to downcast (from base to
derived) for a non-polymorphic class type.