Bridge Design Pattern in C++

Bridge design pattern demo

Discussion. The motivation is to decouple the Time interface from the Time implementation, while still allowing the abstraction and the realization to each be modelled with their own inheritance hierarchy. The implementation classes below are straight-forward. The interface classes are a little more subtle. Routinely, a Bridge pattern interface hierarchy “has a” implementation class. Here the interface base class “has a” a pointer to the implementation base class, and each class in the interface hierarchy is responsible for populating the base class pointer with the correct concrete implementation class. Then all requests from the client are simply delegated by the interface class to the encapsulated implementation class.

#include <iostream.h>
#include <iomanip.h>
#include <string.h>

class TimeImp {
  public:
    TimeImp(int hr, int min) {
        hr_ = hr;
        min_ = min;
    }
    virtual void tell() {
        cout << "time is " << setw(2) << setfill(48) << hr_ << min_ << endl;
    }
  protected:
    int hr_, min_;
};

class CivilianTimeImp: public TimeImp {
  public:
    CivilianTimeImp(int hr, int min, int pm): TimeImp(hr, min) {
        if (pm)
          strcpy(whichM_, " PM");
        else
          strcpy(whichM_, " AM");
    }

    /* virtual */
    void tell() {
        cout << "time is " << hr_ << ":" << min_ << whichM_ << endl;
    }
  protected:
    char whichM_[4];
};

class ZuluTimeImp: public TimeImp {
  public:
    ZuluTimeImp(int hr, int min, int zone): TimeImp(hr, min) {
        if (zone == 5)
          strcpy(zone_, " Eastern Standard Time");
        else if (zone == 6)
          strcpy(zone_, " Central Standard Time");
    }

    /* virtual */
    void tell() {
        cout << "time is " << setw(2) << setfill(48) << hr_ << min_ << zone_ <<
          endl;
    }
  protected:
    char zone_[30];
};

class Time {
  public:
    Time(){}
    Time(int hr, int min) {
        imp_ = new TimeImp(hr, min);
    }
    virtual void tell() {
        imp_->tell();
    }
  protected:
    TimeImp *imp_;
};

class CivilianTime: public Time {
  public:
    CivilianTime(int hr, int min, int pm) {
        imp_ = new CivilianTimeImp(hr, min, pm);
    }
};

class ZuluTime: public Time {
  public:
    ZuluTime(int hr, int min, int zone) {
        imp_ = new ZuluTimeImp(hr, min, zone);
    }
};

int main() {
  Time *times[3];
  times[0] = new Time(14, 30);
  times[1] = new CivilianTime(2, 30, 1);
  times[2] = new ZuluTime(14, 30, 6);
  for (int i = 0; i < 3; i++)
    times[i]->tell();
}

Output

time is 1430
time is 2:30 PM
time is 1430 Central Standard Time

Code examples