Why trivial copyable class require the destructor must be trivial

Question

Base on the C++ standard. The trivial copyable class are define as following:

According to 9/5,

A trivially copyable class is a class that:
- has no non-trivial copy constructors (12.8),
- has no non-trivial move constructors (12.8),
- has no non-trivial copy assignment operators (13.5.3, 12.8),
- has no non-trivial move assignment operators (13.5.3, 12.8), and
- has a trivial destructor (12.4).

By my understanding, the trivially copyable class is which can be copied by bitwise copied. So what's the intuition and reason to require trivial destructor which is unrelated to the bitwise copy.

Answer 1

The reason is simple enough. Trivially copyable means that it is valid and defined behaviour to copy one object A over the top of another B. Obviously the destructor for B will not be called, so it has to be trivial.

There is a description of object lifetime at N3797 3.8/4 which appears to cover the situation. However, there could be a loophole regarding reuse of storage and non-calling of non-trivial destructor provided the program does not depend on side effects of the destructor.

Answer 2

A non trivial destructor likely implies you are deleting some pointers. If this is the case it seems error prone to do a bitwise copy of the class since you'd then have two instances that will both try to delete the same pointer.

This is just a guess though