一.傳統(tǒng)多態(tài)->動多態(tài)

代碼示例:

// 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; … };

調用示例:

// 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.靜多態(tài)=>模版

不再需要繼承

// 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.比較

動多態(tài):1.需要一個公共基類,2.運行時動態(tài)綁定3.生成代碼比較小 4.不需要發(fā)布源代碼

靜多態(tài):1.不需要繼承關系,2.編譯時綁定 3.體積大,執(zhí)行速度效率高

自有優(yōu)缺點

總結

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