[设计模式] 7 桥接模式 bridge

#include<iostream>
using namespace std;

class AbstractionImp
{
    public:
        virtual ~AbstractionImp();
        virtual void Operation() = ;
    protected:
        AbstractionImp();
    private:
};

class Abstraction
{
    public:
        virtual ~Abstraction();

        virtual void Operation() = ;

    protected:
        Abstraction();

    private:

};

class RefinedAbstraction:public Abstraction
{
    public:
        RefinedAbstraction(AbstractionImp* imp);

        ~RefinedAbstraction();

        void Operation();

    protected:

    private:
        AbstractionImp* _imp;

};

Abstraction::Abstraction()
{

}

Abstraction::~Abstraction()
{

}

RefinedAbstraction::RefinedAbstraction(AbstractionImp* imp)
{
    _imp = imp;
}

RefinedAbstraction::~RefinedAbstraction()
{

}

void RefinedAbstraction::Operation()
{
    _imp->Operation();
}

class  ConcreteAbstractionImpA:public AbstractionImp
{
    public:
        ConcreteAbstractionImpA();
        ~ConcreteAbstractionImpA();
        virtual void Operation();
    protected:
    private:
};
class  ConcreteAbstractionImpB:public AbstractionImp
{
    public:
        ConcreteAbstractionImpB();
        ~ConcreteAbstractionImpB();
        virtual void Operation();
    protected:
    private:
};

AbstractionImp::AbstractionImp()
{
}
AbstractionImp::~AbstractionImp()
{
}
void AbstractionImp::Operation()
{
    cout<<"AbstractionImp....imp..."<<endl;
}
    ConcreteAbstractionImpA::ConcreteAbstractionImpA()
{
}
ConcreteAbstractionImpA::~ConcreteAbstractionImpA()
{
}
void ConcreteAbstractionImpA::Operation()
{
    cout<<"ConcreteAbstractionImpA...."<<endl;
}
ConcreteAbstractionImpB::ConcreteAbstractionImpB()
{
}
ConcreteAbstractionImpB::~ConcreteAbstractionImpB()
{
}
void ConcreteAbstractionImpB::Operation()
{
    cout<<"ConcreteAbstractionImpB...."<<endl;
}

int main(int argc,char* argv[])
{
    AbstractionImp*  imp  =  new ConcreteAbstractionImpA();
    Abstraction*  abs  =  new RefinedAbstraction(imp);
    abs->Operation();

    imp  =  new ConcreteAbstractionImpB();
    abs  =  new RefinedAbstraction(imp);
    abs->Operation();

    return ;
}

输出：

ConcreteAbstractionImpA....
ConcreteAbstractionImpB....

[DP]书上定义：将抽象部分与它的实现部分分离，使它们都可以独立地变化。考虑装操作系统，有多种配置的计算机，同样也有多款操作系统。如何运用桥接模式呢？可以将操作系统和计算机分别抽象出来，让它们各自发展，减少它们的耦合度。当然了，两者之间有标准的接口。这样设计，不论是对于计算机，还是操作系统都是非常有利的。下面给出这种设计的UML图，其实就是桥接模式的UML图。

给出C++的一种实现：

#include<iostream>
using namespace std;

class OS
{
    public:
        virtual void InstallOS_Imp() {}
};
class WindowOS: public OS
{
    public:
        void InstallOS_Imp() { cout<<"Install window OS"<<endl; }
};
class LinuxOS: public OS
{
    public:
        void InstallOS_Imp() { cout<<"Install Linux OS"<<endl; }
};
class UnixOS: public OS
{
    public:
        void InstallOS_Imp() { cout<<"Install UnixOS" <<endl; }
};

class Computer
{
    public:
        virtual void InstallOS(OS *os) {}
};
class DellComputer: public Computer
{
    public:
        void InstallOS(OS *os) { os->InstallOS_Imp(); }
};
class AppleComputer: public Computer
{
    public:
        void InstallOS(OS *os) { os->InstallOS_Imp(); }
};
class HPComputer: public Computer
{
    public:
        void InstallOS(OS *os) { os->InstallOS_Imp(); }
};

int main()
{
    OS *os1 = new WindowOS();
    OS *os2 = new LinuxOS();
    Computer *computer1 = new AppleComputer();
    Computer *computer2 = new HPComputer();
    computer1->InstallOS(os1);
    computer2->InstallOS(os2);
}

输出：

Install window OS
Install Linux OS

Bridge 是设计模式中比较复杂和难理解的模式之一，也是 OO 开发与设计中经常会用到
的模式之一。使用组合（委托）的方式将抽象和实现彻底地解耦，这样的好处是抽象和实现
可以分别独立地变化，系统的耦合性也得到了很好的降低。
GoF 在说明 Bridge 模式时，在意图中指出 Bridge 模式“将抽象部分与它的实现部分分
离，使得它们可以独立地变化”。

实际上上面使用 Bridge 模式和使用带来问题方式的解决方案的根本区别在于是通过继
承还是通过组合的方式去实现一个功能需求。因此面向对象分析和设计中有一个原则就是：
Favor Composition Over Inheritance。