介紹

參與者

實現(xiàn)代碼

#include <iostream>
#include <map>

class Context;
class  Expression {
public:
    virtual int interpreter(Context *) = 0;//一定會有解釋方法
    virtual  ~Expression() = default;
};
class Context{
public:
    int getVal(Expression *expression)
    {
        auto it = m.find(expression);
        if(m.end() != it)
        {
            return it->second;
        }
        return 0;
    }
    void insert(Expression *expression,int val)
    {
        m.insert(std::make_pair(expression,val));
    }
private:
    std::map<Expression*,int> m;
};
class TerminalExpression :public  Expression{
public:
    explicit TerminalExpression(std::string name_)
    {
        name = name_;
    }
    int interpreter(Context *context) override
    {
        return context->getVal(this);
    }
    ~TerminalExpression() override = default;
private:
    std::string name;
};
class NonTerminalExpressinon : public Expression{
public:
    NonTerminalExpressinon(Expression *ee1,Expression *ee2)
    {
        e1 = ee1;
        e2 = ee2;
    }
    Expression *e1;
    Expression *e2;
    int interpreter(Context *context) override
    {
        return 0;
    }
    ~NonTerminalExpressinon() override = default;
};

class Plus : public NonTerminalExpressinon {
public:
    Plus(Expression *ee1,Expression *ee2):NonTerminalExpressinon(ee1,ee2)
    {

    }
    int interpreter(Context *context) override
    {
        return e1->interpreter(context) + e2->interpreter(context);
    }
    ~Plus() override = default;
};

class Minus : public  NonTerminalExpressinon {
public:
    Minus(Expression *ee1,Expression *ee2):NonTerminalExpressinon(ee1,ee2)
    {

    }
    int interpreter(Context *context) override
    {
        return e1->interpreter(context) - e2->interpreter(context);
    }
    ~Minus() override = default;
};
int main()
{
    auto *context = new Context();
    Expression *e1 = new TerminalExpression("a");
    Expression *e2 = new TerminalExpression("b");
    Expression *e3 = new TerminalExpression("c");
    context->insert(e1,44);
    context->insert(e2,55);
    context->insert(e3,77);
    Expression* plus = new Plus(new Minus(e1,e2),e3);
    auto ret = plus->interpreter(context);
    std::cout<<"輸出結(jié)果為："<<ret<<std::endl;
}

輸出結(jié)果

輸出結(jié)果為：66

特點

參考

• https://blog.csdn.net/niunai112/article/details/79982712#%E7%9B%AE%E5%BD%95
• http://baijiahao.baidu.com/s?id=1602346331901148023&wfr=spider&for=pc