default override of virtual destructor

Question

Everyone knows that the desructor of base class usually has to be virtual. But what is about the destructor of derived class? In C++11 we have keyword \"override\" and ability t

Answer 1

There is (at least) one reason for using override here -- you ensure that the base class's destructor is always virtual. It will be a compilation error if the derived class's destructor believes it is overriding something, but there is nothing to override. It also gives you a convenient place to leave generated documentation, if you're doing that.

On the other hand, I can think of two reasons not to do this:

• It's a little weird and backwards for the derived class to enforce behavior from the base class.

• If you define a destuctor in the header (or if you make it inline), you do introduce the possibility for odd compilation errors. Let's say your class looks like this:

  struct derived {
      struct impl;
      std::unique_ptr m_impl;
      ~derived() override = default;
  };
  

  You will likely get a compiler error because the destructor (which is inline with the class here) will be looking for the destructor for the incomplete class, derived::impl.

  This is my round-about way of saying that every line of code can become a liability, and perhaps it's best to just skip something if it functionally does nothing. If you really really need to enforce a virtual destructor in the base class from the parent class, someone suggested using static_assert in concert with std::has_virtual_destructor, which will produce more consistent results, IMHO.