Copy-Control Members

Given our alloc_n_copy and free members, the copy-control members of our class are straightforward. The copy constructor calls alloc_n_copy:

StrVec::StrVec(const StrVec &s)
{
    // call alloc_n_copy to allocate exactly as many elements as in s
    auto newdata = alloc_n_copy(s.begin(), s.end());
    elements = newdata.first;
    first_free = cap = newdata.second;
}

and assigns the results from that call to the data members. The return value from alloc_n_copy is a pair of pointers. The first pointer points to the first constructed element and the second points just past the last constructed element. Because alloc_n_copy allocates space for exactly as many elements as it is given, cap also points just past the last constructed element.

The destructor calls free:

StrVec::~StrVec() { free(); }

The copy-assignment operator calls alloc_n_copy before freeing its existing elements. By doing so it protects against self-assignment:

StrVec &StrVec::operator=(const StrVec &rhs)
{
    // call alloc_n_copy to allocate exactly as many elements as in rhs
    auto data = alloc_n_copy(rhs.begin(), rhs.end());
    free();
    elements = data.first;
    first_free = cap = data.second;
    return *this;
}

Like the copy constructor, the copy-assignment operator uses the values returned from alloc_n_copy to initialize its pointers.