Do derived classes need to implement move semantics when a base provides it?

Question

I finished reading Thomas Becker's "C++ Rvalue References". I have a couple questions on Rvalues and Rvalue references.

Suppose I have a simple array class:

template <class T>
MyArray
{
    ...
    T* m_ptr;  // Pointer to elements
    size_t m_count; // Count of elements
};

Further suppose it provides:

#if(__cplusplus >= 201103L)
MyArray(MyArray&& t)
  : m_ptr(std::move(t.m_ptr)), m_count(std::move(t.m_count))
{
    t.m_ptr = NULL;
    t.m_count = 0;
}
MyArray operator=(MyArray&& t)
{
    std::swap(*this, t);
    return *this;
}
#endif

Now, suppose I have a derived class that does not add new data members:

MyImprovedArray : public MyArray
{
    ...
};

What is required of MyImprovedArray?

Does it need a MyImprovedArray(MyImprovedArray&&) and MyImprovedArray& operator=(MyImprovedArray&&) also? If so, does it only need to perform the base class std::move? Or does it need to perform the std::swap too?

MyImprovedArray(MyImprovedArray&& t)
    : MyArray(t)
{
}

Answer 1

Rule of five (or zero) applies to the derived class, regardless of what the base class defines.

If your derived MyImprovedArray's move constructor isn't going to do anything special, don't define it, and let the compiler generate one.