C++沉思录

第五章 代理类 :

为了实现容器或数组的多态性。

#include <iostream>

using namespace std;

class Vehicle
{
public:
    virtual void start() const = 0 ;
    virtual Vehicle* copy() const = 0 ;
    virtual ~Vehicle() {};
};


class AutoVehicle : public Vehicle 
{
public:
    void start() const
    {
        cout << "start " << endl;
    }
    Vehicle* copy() const
    {
        return new AutoVehicle(* this );
    }
    ~AutoVehicle(){}
};

class Car : public AutoVehicle
{
public:
    void start() const
    {
        cout << " car start " << endl;
    }
    Vehicle* copy() const
    {
        return new Car( *this );
    }
    ~Car(){}
};

class Truck : public AutoVehicle
{
public:
    void start() const
    {
        cout << " truck start " << endl;
    }
    Vehicle* copy() const
    {
        return new Truck( *this );
    }
    ~Truck(){};
};

#include "vehicle.h"

class VehicleSurrogate
{
public :
    VehicleSurrogate();
    VehicleSurrogate( const Vehicle&);
    VehicleSurrogate( const VehicleSurrogate&);
    VehicleSurrogate& operator= ( const VehicleSurrogate&);
    ~VehicleSurrogate();
    void start();
private:
    Vehicle* vp;
};
VehicleSurrogate::VehicleSurrogate() : vp ( NULL){}
VehicleSurrogate::VehicleSurrogate(const Vehicle& v)
{
    vp = v.copy();
}
VehicleSurrogate::VehicleSurrogate(const VehicleSurrogate& v) : vp(v.vp ? v.vp->copy() : NULL) {};
VehicleSurrogate& VehicleSurrogate::operator=( const VehicleSurrogate& v)
{
    if ( this != &v )
    {
        delete vp;
        vp = (v.vp ? v.vp->copy() : NULL);
    }
    return *this;
}
void VehicleSurrogate::start()
{
    if ( vp == NULL )
        throw "empty";
    
        vp->start();
}
VehicleSurrogate::~VehicleSurrogate()
{
    delete vp;
}

#include "VehicleSurrogate.h"

int main()
{
    
    VehicleSurrogate parking_lot[100];
    Car x;
    Truck t;
    parking_lot[0] = VehicleSurrogate( x);
    parking_lot[1] = VehicleSurrogate( t);
    parking_lot[0].start();
    parking_lot[1].start();
    
    return 0 ;
}