class vector {
    int sz;
    double* elem;
    void copy(const vector& arg);     // copy elements from arg into *elem
public:
    vector(int s) :sz(s), elem(new double[s]) { } // constructor
    ~vector() { delete[] elem; }                  // destructor
   // int size() const { return sz; }               // the current size
    double get(int n) { return elem[n]; }         // access: read
    void set(int n, double v) { elem[n]=v; }      // access: write
    vector& operator=(const vector&);            
};
请问各位vector& operator=(const vector&); 这句从语法上怎么解释，谢谢

vector& vector::operator=(const vector& a)
// make this vector a copy of a
{
    double* p = new double[a.sz];     // allocate new space
    copy(a);                          // copy elements
    delete[ ] elem;                   // deallocate old space
    elem = p;                         // now we can re-set elem
    sz = a.sz;
    return *this;                     
}
这样可以吗？

vector& operator=(const vector&); 那此时的operator只是一个vector&的变量，那它怎么又可以定义啊？？？