Design mode C + + description----09. Bridging (bridge) mode __c++

I. Examples

N years ago:

When the computer first comes out, software and hardware are tied together, such as IBM out of a computer, there is a custom system, if called Ibm_win, this ibm_win system of course can not run on HP computers, the same HP out of the Hp_win system can not run on IBM.

If a new company, Apple, had a new computer, the company would also develop its own system apple_win,apple_linux.

In fact, the software and hardware developed by several companies are similar in many places, and if each company is doing its own system, it means a huge waste of resources and people.

At this point, regardless of the emergence of new systems, or the emergence of new companies, this design pattern changes are very large.

n years later:

Windows appears, Linux appears, and software and hardware are finally separated. Systems such as Windows can run on IBM machines as well as on HP machines.

The software is focused on the software and the hardware is focused on the hardware. That's why the computer system has been growing (more focused) and the reason it's driving more companies (less expensive).

Whether it's a new hardware platform or a new OS, everyone can focus on their own domain. That is, the external changes are very large, but the impact on this model is very small.

Code implementation:

Operating system
class OS  
{public  
:  
    virtual void Run () {}  
};

Windows
class Windowos:public OS  
{public
:
    void Run () {cout<< run Windows <<endl;}   
} ;

Linux
class Linuxos:public OS  
{public
:
    void Run () {cout<< "Running Linux" <<endl;}   
};

//Computer
class Computer  
{public
:
    virtual void Installos (OS *os) {}  
};

IBM computer
class Ibmcomputer:public Computer  
{public
:
    void Installos (OS *os) {Os->run ();}  
};

HP computer
class Hpcomputer:public Computer  
{public
:
    void Installos (OS *os) {Os->run ();}  
};  


int main ()  
{  
    OS *os1 = new Windowos ();
    OS *os2 = new Linuxos ();
    
    Computer *computer1 = new Ibmcomputer ();
    Computer1->installos (OS1);
    Computer1->installos (OS2);

    return 0;
}

Two. Bridging mode

Definition: separates the abstract part from its implementation, so that they can all change independently .

In other words, it is to make the implementation independent, so that they change, without affecting other implementations, so as to reduce the coupling.

Why is it called bridge mode, as can be seen from the above figure, it is like a bridges, the bridge on both sides of the system is relatively independent, the left is an abstract part, the right is the implementation part.

three. Combinatorial, aggregate reuse principle

From the above two kinds of structural graphs, we can draw a principle: try to use composition, aggregation, try not to use class inheritance.