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Subject: [std-proposals] Make abstract classes non-deletable if no virtual destructor available
From: Kilian Henneberger (kilis-mail_at_[hidden])
Date: 2020-03-23 15:19:24


Hello,

an abstract class (a class that either defines or inherits at least one
function for which the final overrider is pure virtual)
cannot be instantiated. However it can be destroyed. But deleting a
Derived-object through a pointer to Base-object
leads to undefined behaviour if the destructor of the Base-class is not
virtual.
There also exists a CppCoreGuideline addressing this topic:
http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-dtor-virtual

I want to propose that we make the attempt to delete a pointer to an
abstract class ill-formed,
if the abstract class does not have a (public) virtual destructor.

This would turn what currently is UB into a compiler error.
But it also might imply that code which compiles today (even if leading
to UB), wont compile any longer after this change.

I am looking forward to any feedback.
Best regards,
Kilian Henneberger


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