C++ Primer 第四版文本查询示例的问题

class Query {
// these operators need access to the Query_base* constructor
friend Query operator~(const Query &);
friend Query operator|(const Query&, const Query&);
friend Query operator&(const Query&, const Query&);
public:
Query(const std::string&); // builds a new WordQuery

// copy control to manage pointers and use counting
Query(const Query &c): q(c.q), use(c.use) { ++*use; }
~Query() { decr_use(); }
Query& operator=(const Query&);

// interface functions: will call corresponding Query_base operations
std::set<TextQuery::line_no>
eval(const TextQuery &t) const { return q->eval(t); }
std::ostream &display(std::ostream &os) const
{ return q->display(os); }
private:
Query(Query_base *query): q(query),
use(new std::size_t(1)) { }
Query_base *q;
std::size_t *use;
void decr_use()
{ if (--*use == 0) { delete q; delete use; } }
};

class NotQuery: public Query_base {
friend Query operator~(const Query &);
NotQuery(Query q): query(q) { }

// concrete class: NotQuery defines all inherited pure virtual functions
std::set<line_no> eval(const TextQuery&) const;
std::ostream& display(std::ostream &os) const
{ return os << "~(" << query << ")"; }
const Query query;
};

class BinaryQuery: public Query_base {
protected:
BinaryQuery(Query left, Query right, std::string op):
lhs(left), rhs(right), oper(op) { }

// abstract class: BinaryQuery doesn't define eval
std::ostream& display(std::ostream &os) const
{ return os << "(" << lhs << " " << oper << " "
<< rhs << ")"; }

const Query lhs, rhs; // right- and left-hand operands
const std::string oper; // name of the operator
};

class AndQuery: public BinaryQuery {
friend Query operator&(const Query&, const Query&);
AndQuery(Query left, Query right):
BinaryQuery(left, right, "&") { }

// concrete class: AndQuery inherits display and defines remaining pure virtual
std::set<line_no> eval(const TextQuery&) const;
};

class OrQuery: public BinaryQuery {
friend Query operator|(const Query&, const Query&);
OrQuery(Query left, Query right): BinaryQuery(left, right, "|") { }

// concrete class: OrQuery inherits display and defines remaining pure virtual
std::set<line_no> eval(const TextQuery&) const;
};

inline Query operator&(const Query &lhs, const Query &rhs)
{
return new AndQuery(lhs, rhs);
}

inline Query operator|(const Query &lhs, const Query &rhs)
{
return new OrQuery(lhs, rhs);
}

inline Query operator~(const Query &oper)
{
return new NotQuery(oper);
｝


这上面把~|&设为友元说是会用到
Query(Query_base *query): q(query),
use(new std::size_t(1)) { }
这个构造函数，但是我怎么都看不出有用到这个构造函数。
求解……