C++沉思录

第五章代理类 :

为了实现容器或数组的多态性。

 1 #include <iostream>
 2 
 3 using namespace std;
 4 
 5 class Vehicle
 6 {
 7 public:
 8     virtual void start() const = 0 ;
 9     virtual Vehicle* copy() const = 0 ;
10     virtual ~Vehicle() {};
11 };
12 
13 
14 class AutoVehicle : public Vehicle 
15 {
16 public:
17     void start() const
18     {
19         cout << "start " << endl;
20     }
21     Vehicle* copy() const
22     {
23         return new AutoVehicle(* this );
24     }
25     ~AutoVehicle(){}
26 };
27 
28 class Car : public AutoVehicle
29 {
30 public:
31     void start() const
32     {
33         cout << " car start " << endl;
34     }
35     Vehicle* copy() const
36     {
37         return new Car( *this );
38     }
39     ~Car(){}
40 };
41 
42 class Truck : public AutoVehicle
43 {
44 public:
45     void start() const
46     {
47         cout << " truck start " << endl;
48     }
49     Vehicle* copy() const
50     {
51         return new Truck( *this );
52     }
53     ~Truck(){};
54 };

 1 #include "vehicle.h"
 2 
 3 class VehicleSurrogate
 4 {
 5 public :
 6     VehicleSurrogate();
 7     VehicleSurrogate( const Vehicle&);
 8     VehicleSurrogate( const VehicleSurrogate&);
 9     VehicleSurrogate& operator= ( const VehicleSurrogate&);
10     ~VehicleSurrogate();
11     void start();
12 private:
13     Vehicle* vp;
14 };
15 VehicleSurrogate::VehicleSurrogate() : vp ( NULL){}
16 VehicleSurrogate::VehicleSurrogate(const Vehicle& v)
17 {
18     vp = v.copy();
19 }
20 VehicleSurrogate::VehicleSurrogate(const VehicleSurrogate& v) : vp(v.vp ? v.vp->copy() : NULL) {};
21 VehicleSurrogate& VehicleSurrogate::operator=( const VehicleSurrogate& v)
22 {
23     if ( this != &v )
24     {
25         delete vp;
26         vp = (v.vp ? v.vp->copy() : NULL);
27     }
28     return *this;
29 }
30 void VehicleSurrogate::start()
31 {
32     if ( vp == NULL )
33         throw "empty";
34     
35         vp->start();
36 }
37 VehicleSurrogate::~VehicleSurrogate()
38 {
39     delete vp;
40 }

 1 #include "VehicleSurrogate.h"
 2 
 3 int main()
 4 {
 5     
 6     VehicleSurrogate parking_lot[100];
 7     Car x;
 8     Truck t;
 9     parking_lot[0] = VehicleSurrogate( x);
10     parking_lot[1] = VehicleSurrogate( t);
11     parking_lot[0].start();
12     parking_lot[1].start();
13     
14     return 0 ;
15 }