Do C++ abstract classes need to obey the rule of five?

Question

When implementing an abstract class like this:

class Base
{
public:
    virtual ~Base() = default;
    virtual void foo() = 0;
};

Does this interface have to obey the rule of five i.e. do I have to add a copy constructor, copy assignment operator, move constructor and move assignment operator?

I'd figure that an instace of type Base can not be instantiated due to the pure virtual member function and thus providing default implementations for the other special member functions might serve no real purpose.

Is there any use-case/example that would require me to provide the other special member functions?

Answer 1

"abstract" is irrelevant here. A class needs its own copy constructor, copy assignment operator, etc. if it has data that won't be properly copied by the default versions. Full stop. The presence or absence of pure virtual functions does not change this. Your example doesn't have any data, so doesn't have an issue here.