解释器模式-c++实现

还是挺有意思的

// InterpreterPattern.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>  
#include <map>  
#include <string>  

using namespace std;

class Context
{
private:
map<string, int> valueMap;

public:
void addValue(string key, int value)
{
valueMap.insert(std::pair<string, int>(key, value));
}

int getValue(string key)
{
return valueMap[key];
}
};

class AbstractExpression
{
public:
virtual int interpreter(Context context) = 0;
};

class AddNonterminalExpression : public AbstractExpression
{
private:
AbstractExpression *left;
AbstractExpression *right;

public:
AddNonterminalExpression(AbstractExpression *left, AbstractExpression *right)
{
this->left = left;
this->right = right;
}

int interpreter(Context context)
{
return this->left->interpreter(context) + this->right->interpreter(context);
}

};

class SubtractNonterminalExpression : public AbstractExpression
{
private:
AbstractExpression *left;
AbstractExpression *right;

public:
SubtractNonterminalExpression(AbstractExpression *left, AbstractExpression *right)
{
this->left = left;
this->right = right;
}

int interpreter(Context context)
{
return this->left->interpreter(context) - this->right->interpreter(context);
}

};

class TerminalExpression : public AbstractExpression
{
private:
int i;

public:
TerminalExpression(int i)
{
this->i = i;
}

int interpreter(Context context)
{
return this->i;
}
};

int main() {
//a-b+c
Context context;
context.addValue("a", 7);
context.addValue("b", 8);
context.addValue("c", 2);

SubtractNonterminalExpression *subtractValue = new SubtractNonterminalExpression(new TerminalExpression(
context.getValue("a")), new TerminalExpression(context.getValue("b")));

AddNonterminalExpression *addValue = new AddNonterminalExpression(subtractValue, new TerminalExpression(
context.getValue("c")));

cout << addValue->interpreter(context)<<endl;

return 0;
}