custom vector copy constructor, PPP2 Chapter 18 Section 18.3.1

[Osman Zakir]

Dr. Stroustrup didn't show an overloaded operator+ for the vector class, so how do I get this to work?

vector:: vector(const vector& arg)
    // allocate elements, then initialize them by copying
    :sz{arg.sz}, elem{new double[arg.sz]}
{
    copy(arg,arg+sz,elem); // std::copy(); see §B.5.2
}

I tried to overload the operator (+) for it, but I got two error messages, both basically saying that there's no such iterator_category tag as the one I'm trying to use.  How do I define an iterator_category tag for this class, if that's what I have to do?  

As for the class itself, this is what I have right now:

// a very simplified vector of doubles (like vector<double>)

class vector
{
 int sz;           // the size
 double *elem;         // pointer to the first element (of type double)
public:
 vector(int s);
 vector(std::initializer_list<double> lst);
 //vector(const vector&);       // copy constructor: define copy
 vector &operator=(const vector &);    // copy assignment
 vector operator()(double val) { return val; }
 ~vector() { delete[] elem; }
 int size() const { return sz; }     // return current size
 double get(int n) const { return elem[n]; }  // access: read
 void set(int n, double v) { elem[n] = v; }  // access: write
};

Someone please help.  Thanks in advance.

[Christiano]

Read:
https://chcpp.info/index.php/2017/09/12/programming-principles-and-practice-using-c-2nd-edition-bugs/

 Page 633
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In the code:

vector:: vector(const vector& arg)
// allocate elements, then initialize them by copying
          :sz{arg.sz}, elem{new double[arg.sz]}
{
          copy(arg.elem,arg.elem.sz,elem);  // std::copy(); see §B.5.2
}

The copy line should be:
copy(arg.elem,arg.elem+sz,elem);