ChainofResponsibility - shoonie/StudyingDesignPattern GitHub Wiki

Intent

Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

Diagram

disgram

Consequences

Reduced coupling.
Added flexibility in assigning responsibilities to objects.
Receipt isn't guaranteed.

Implementation

Implementing the successor chain.
Connecting successors.
Representing requests.

Sample Code

\\ http://www.bogotobogo.com/DesignPatterns/chain_of_responsibility.php
#include <iostream>
#include <string>
using namespace std;

class Photo 
{
public:
    Photo(string s) : mTitle(s) 
    {
	cout << "Processing " << mTitle << " ...\n";
    }

private:
    string mTitle;
};

class PhotoProcessor
{
public:
    PhotoProcessor() : mNextProcessor(0){ }

public:
    void process(Photo &p;) {
        processImplementation(p);
        if (mNextProcessor != 0) 
            mNextProcessor->process(p);
    }

    virtual ~PhotoProcessor() { }

    void setNextProcessor(PhotoProcessor *p) {
        mNextProcessor = p;
    }

protected:
    virtual void processImplementation(Photo &a;) = 0;

private:
    PhotoProcessor *mNextProcessor;
};

class Scale : public PhotoProcessor
{
public:
    enum SCALE { S50, S100, S200, S300, S500 };
    Scale(SCALE s) : mSCALE(s) { }

private:
    void processImplementation(Photo &a;) {
        cout << "Scaling photo\n";
    }

    SCALE mSCALE;
};

class RedEye : public PhotoProcessor
{
private:
    void processImplementation(Photo &a;) {
        cout << "Removing red eye\n";
    }
};

class Filter : public PhotoProcessor
{
private:
    void processImplementation(Photo &a;) {
        cout << "Applying filters\n";
    }
};

class ColorMatch : public PhotoProcessor
{
private:
    void processImplementation(Photo &a;)
    {
        cout << "Matching colors\n";
    }
};

void processPhoto(Photo &photo;)
{   
    ColorMatch match;
    RedEye eye;
    Filter filter;
    Scale scale(Scale::S200);
    scale.setNextProcessor(&eye;);
    eye.setNextProcessor(&match;);
    match.setNextProcessor(&filter;);
    scale.process(photo);
}

int main()
{
    Photo *p = new Photo("Y2013 Photo");
    processPhoto(*p);
    return 0;
}