C++ Primer（第5版） 练习 15.35

练习 15.35 实现Query类和Query_base类，其中需要定义rep而无须定义eval。

环境：Linux Ubuntu（云服务器）

工具：vim

 

代码块：

#include<iostream>
#include<vector>
#include<memory>
using namespace std;class Query_base{friend class Query;protected:using line_no = TextQuery::line::no;virtual ~Query_base() = default;private:virtual QueryResult eval(const TextQuery &)const = 0;virtual std::string rep() const = 0;
};class Query{friend Query operator~(const Query &);friend Query operator|(const Query&, const Query&);friend Query operator&(const Query&, const Query&);public:Query(const std::string);QueryResult eval(const TextQuery &t) const { return q->eval(t); }std::string rep() const { return q->rep(); }private:Query(std::shared_ptr<Query_base> query): q(query) {}std::shared_ptr<Query_base> q;
};std::ostream &operator<<(std::ostream &os, const Query &query){return os<<query.rep();
}class WordQuery: public Query_base{friend class Query;WordQuery(const std::string &s): query_word(s) {}QueryResult eval(const TextQuery &t) const { return t.query(query_word); }std::string rep() const { return query_word; }std::string query_word;
};inline Query::Query(const std::string &s): q(new WordQuery(s)) {}class NotQuery: public Query_base{friend Query operator~(const Query &);NotQuery(const Query &q): query(q) {}std::string rep() const { return "~(" + query.rep() + ")"; }QueryResult eval(const TextQuery&) const;Query query;
}inline Query operator~(const Query &operand){return std::shared_ptr<Query_base>(new NotQuery(operand));
}class BinaryQuery: public Query_base{protected:BinaryQuery(const Query &l, const Query &r, std::string s): lhs(l), rhs(r), opSym(s) {}std::string rep() const { return "(" + lhs.rep() + " " + opSym + " " + rhs.rep() + ")"; }Query lhs, rhs;std::string opSym;
};class AndQuery: public BinaryQuery{friend Query operator&(const Query &, const Query &);AndQuery(const Query &left, const Query &right): BinaryQuery(left, right, "&") {}QueryResult eval(const TextQuery&) const;
};inline Query operator&(const Query &lhs, const Query &rhs){return std::shared_ptr<Query_base>(new AndQuery(lhs, rhs));
}class OrQuery: public BinaryQuery{friend Query operator|(const Query &, const Query &);OrQuery(const Query &left, const Query &right): BinaryQuery(left, right, "|") {}QueryResult eval(const TextQuery&) const;
};inline Query operator|(const Query &lhs, const Query &rhs){return std::shared_ptr<Query_base>(new OrQuery(lhs, rhs));
}