一.传统多态->动多态

代码示例:

// common abstract base class GeoObj for geometric objects
class GeoObj {
public: // draw geometric object: virtual void draw() const = 0; // return center of gravity of geometric object: virtual Coord center_of_gravity() const = 0; …
}; // concrete geometric object class Circle
// - derived from GeoObj
class Circle : public GeoObj {
public: virtual void draw() const; virtual Coord center_of_gravity() const; …
}; // concrete geometric object class Line
// - derived from GeoObj
class Line : public GeoObj {
public: virtual void draw() const; virtual Coord center_of_gravity() const; …
};

调用示例:

// draw any GeoObj
void myDraw (GeoObj const& obj)
{ obj.draw();            // call draw() according to type of object
} // process distance of center of gravity between two GeoObjs
Coord distance (GeoObj const& x1, GeoObj const& x2)
{ Coord c = x1.center_of_gravity() - x2.center_of_gravity(); return c.abs();        // return coordinates as absolute values
} // draw inhomogeneous collection of GeoObjs
void drawElems (std::vector<GeoObj*> const& elems)
{ for (unsigned i=0; i<elems.size(); ++i) { elems[i]->draw();  // call draw() according to type of element }
}
int main()
{ Line l; Circle c, c1, c2; myDraw(l);            // myDraw(GeoObj&) => Line::draw() myDraw(c);            // myDraw(GeoObj&) => Circle::draw() distance(c1,c2);      // distance(GeoObj&,GeoObj&) distance(l,c);        // distance(GeoObj&,GeoObj&) std::vector<GeoObj*> coll;  // inhomogeneous collection coll.push_back(&l);         // insert line coll.push_back(&c);         // insert circle drawElems(coll);            // draw different kinds of GeoObjs
} 

二.静多态=>模版

不再需要继承

// draw any GeoObj
template <typename GeoObj>
void myDraw (GeoObj const& obj)
{ obj.draw();    // call draw() according to type of object
} // process distance of center of gravity between two GeoObjs
template <typename GeoObj1, typename GeoObj2>
Coord distance (GeoObj1 const& x1, GeoObj2 const& x2)
{ Coord c = x1.center_of_gravity() - x2.center_of_gravity(); return c.abs();  // return coordinates as absolute values
} // draw homogeneous collection of GeoObjs
template <typename GeoObj>
void drawElems (std::vector<GeoObj> const& elems)
{ for (unsigned i=0; i<elems.size(); ++i) { elems[i].draw();    // call draw() according to type of element }
} int main()
{ Line l; Circle c, c1, c2; myDraw(l);        // myDraw<Line>(GeoObj&) => Line::draw() myDraw(c);        // myDraw<Circle>(GeoObj&) => Circle::draw() distance(c1,c2);  // distance<Circle,Circle>(GeoObj1&,GeoObj2&) distance(l,c);    // distance<Line,Circle>(GeoObj1&,GeoObj2&) // std::vector<GeoObj*> coll;    // ERROR: no inhomogeneous //        collection possible std::vector<Line> coll;   // OK: homogeneous collection possible coll.push_back(l);        // insert line drawElems(coll);          // draw all lines
}

三.比较

动多态:1.需要一个公共基类,2.运行时动态绑定3.生成代码比较小 4.不需要发布源代码

静多态:1.不需要继承关系,2.编译时绑定 3.体积大,执行速度效率高

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