条款37：绝不重新定义继承而来的缺省参数值

问题代码：

class Shape{public:enum Color{RED,GREEN,BLUE};virtual void draw(Color color = RED)const = 0;...};class Circle:public Shape{public:virtual void draw(Color color = GREEN)const{ ... }};class Rectangle:public Shape{public:virtual void draw(Color color)const{ ... }};Shape* ps;Shape* pc = new Circle;Shape* pr = new Rectangle;//问题pc->draw(); //Circle::draw(RED)

修改后：

class Shape{public:enum Color{RED,GREEN,BLUE};void draw(Color color = RED) const{...doDraw(color);...}...private:virtual void doDraw(Color color) const = 0; };class Circle:public Shape{...private:virtual void doDraw(Color color){ ... }};