Chain of Responsibility

GoF Behavioral Design Pattern

Scenario: User Authentication

Authentication Module

Using email/password

Using Local Network Login/pass

Using Remote login/pass

Let’s code!

This mass is available at https://gist.github.com/hlegius/e1a721ebbc7de2a91fb1

Code Review

• We got a Service class;• Skinny Controllers;• Meaningful (and cool) names;• No temp variable;• Short methods;• A lot of non-sense `ifs` statements;• (Very) Complicated logic. (WTF award!)

So, let’s go forward on that ?

This mass is available at https://gist.github.com/hlegius/e1a721ebbc7de2a91fb1

WTF dude!?

Wrong design decision indicator!

Chain of Responsibility

• Decouple client from receivers when you got more than one object that can handle it;

• Giving you the chance to test each part (sender and receivers) in isolated.

• Create one point of change if new Receiver arrives.

• Added flexibility in assigning responsibilities to objects;

• Boost your code readability like a boss.

This code is available at https://gist.github.com/hlegius/7188168

This code is available at https://gist.github.com/hlegius/7188168

This code is available at https://gist.github.com/hlegius/7188168

Chain of ResponsibilityBad Consequences

• More Lines of Code than first version;• Complex if you have one or two fixes

receivers;• Receipt is not guaranteed that will be handled;

Known Uses

• Handle Events – Also known as “Event Handler” or “Responder”

• ET++ used Chain of Responsibility to handle Graphical Updates. (Took from GoF book)

Macro point of view - UML

Client UserAuthenticator

Handler Authenticator <abstract>

ConcreteHandler1 EmailAuthenticator

ConcreteHandler2 NetworkAuthenticator

ConcreteHandler3 PartnerAuthenticator

Don't get me wrong!

You can apply this with PHP, Python, Ruby and so on.

Thank you!

Reference: GoF bookhttp://programe.me