For the class you wrote for exercise 7.40 in § 7.5.1 (p. 291), decide whether any of the constructors might use delegation. If so, write the delegating constructor(s) for your class

(a) Book

class Book {
    public:
      //Book() : isbn(""), name(""), author(),
      //    publish_year(0), publisher(""), version(0) {}
      Book() : Book("", "", std::vector<std::string>(), 0, "", 0) {}
      Book(const std::string &i, const std::string &n,
           const std::vector<std::string> &au,
           unsigned y, const std::string &p = "", unsigned v = 1)
          : isbn(i), name(n), author(au),
            publish_year(y), publisher(p), version(v) {}
      Book(std::istream &is) {
        is >> isbn >> name;
        std::string s;
        is >> s;
        author.push_back(s);
        is >> publish_year >> publisher >> version;
      }

    private:
      std::string isbn;
      std::string name;
      std::vector<std::string> author;
      unsigned publish_year;
      std::string publisher;
      unsigned version;
    };

(b) Date

(c) Employee

(d) Vehicle

(e) Object

(f) Tree