Algorithms that affect object lifetime

The <memory> header provides an obscure family of algorithms with names such as std::uninitialized_copy, std::uninitialized_default_construct, and std::destroy (for the full list, consult an online reference such as cppreference.com). Consider the following algorithm that uses explicit destructor calls to destroy the elements of a range:

    template<class T>
    void destroy_at(T *p)
    {
      p->~T();
    }

    template<class FwdIt>
    void destroy(FwdIt first, FwdIt last)
    {
      for ( ; first != last; ++first) {
        std::destroy_at(std::addressof(*first));
      }
    }

Notice that std::addressof(x) is a convenient little helper function that returns the address of its parameter; it's exactly the same thing as &x except in the rare case that x is of some class type that sadistically overloads its own operator&.

And consider this algorithm that uses explicit placement-new syntax to "copy-construct into" the elements...