条款37：绝不重新定义继承而来的缺省参数

 1 #include <iostream>
 2 
 3 class Shape
 4 {
 5 public:
 6     enum ShapeColor{ Red, Green, Blue };
 7     virtual void draw(ShapeColor color = Red) const = 0;
 8 };
 9 
10 class Rectangle : public Shape
11 {
12 public:
13     virtual void draw(ShapeColor color = Green) const;  // 混淆设计：重新定义了继承而来的缺省参数值
14 };
15 void Rectangle::draw(ShapeColor color) const
16 {
17     std::cout << color << std::endl;
18 }
19 
20 class Circle : public Shape
21 {
22 public:
23     virtual void draw(ShapeColor color) const;  //
24 };
25 void Circle::draw(ShapeColor color) const
26 {
27     std::cout << color << std::endl;
28 }
29 
30 int main()
31 {
32     Shape* ps;                             // 静态类型为Shape*
33     Shape* pr = new Rectangle;   　　　　　　// 静态类型为Shape*
34     Shape* pc = new Circle;          　　　 // 静态类型为Shape*
35 
36     pr->draw();                            // 相当于调用了Rectangle::draw(Shape::Red)
37     pr->draw(Rectangle::Green);            // 调用Rectangle::draw(Rectangle::Green)
38     pc->draw(Circle::Blue);                // 调用Circle::draw(Circle::Blue)
39 
40     return 0;
41 }
42