Is CppCoreGuidelines C.21 correct?

Question

While reading the Bjarne Stroustrup\'s CoreCppGuidelines, I have found a guideline which contradicts my experience.

The C.21 requires the following:

Answer 1

I think maybe your second example is a reasonable exception, and, after all, the guideline does say "the odds are...", so there will be some exceptions.

I'm wondering if this slide might help with your first example:

Here are the slides: https://accu.org/content/conf2014/Howard_Hinnant_Accu_2014.pdf

EDIT: For further information regarding the first case, I've since discovered this: C++11 virtual destructors and auto generation of move special functions