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====== Single Responsibility Principle (SRP) ======

===== Variants and Alternative Names =====

  * One Responsibility Rule
  * Separation of Concerns (this originally was a broader term but is mostly used just like SRP)
  * Curly's Law
  * Do One Thing


===== Context =====
/* fill in contexts here: */
  * [[contexts:Object-Oriented Design]]
  * [[contexts:API Design]]
  * [[contexts:Architecture]]
  * [[contexts:User Interface Design]]

===== Principle Statement =====

There should never be more than one reason to change a certain [[glossary:module]].((compare [[http://www.objectmentor.com/resources/articles/srp.pdf|Robert C. Martin: Single Responsibility Principle]]))


===== Description =====

Every module should have one single responsibility. This means two separate concerns/responsibilities/tasks should always be implemented in separate modules. Robert C. Martin defines a "responsibility" as a "reason to change". If a module has several responsibilities, there are several reasons to change this module---namely the requirements for each responsibility may change. On the other hand a reason to change a module also means that it is the responsibility of the module to implement the aspect that is changed.

Depending on whether a module in the given context is a class, a method, a library, etc. (i.e. the level of abstraction), the granularity of what is seen as a responsibility may differ. 


===== Rationale =====

When this rule is not adhered to, one module has several tasks. If one of these tasks changes, there is the risk that this also has an effect on the other task that normally should be independent. Thus unrelated functionality may break.


===== Strategies =====


===== Caveats =====

See section [[#contrary principles]].


===== Origin =====
/* the *primary* source */
{{page>resources:Agile Software Development, Principles, Patterns, and Practices#reference}}

===== Evidence =====
/* Comment out what is not applicable and explain the rest: */
/*  * [[wiki:Proposed]]*/
/*  * [[wiki:Examined]]*/

  * [[wiki:Accepted]]

/*  * [[wiki:Questioned]]*/


===== Relations to Other Principles =====

==== Generalizations ====

  * [[High Cohesion]] (HC)
  * [[Encapsulate the Concept that Varies]] (ECV)
==== Specializations ====

==== Contrary Principles ====

==== Complementary Principles ====


==== Principle Collections ====

{{page>collections:SOLID#Box}}
===== Examples =====


===== Description Status =====
/* Choose one of the following and comment out the rest: */
/*[[wiki:Stub]]*/
[[wiki:Incomplete]]
/*[[wiki:Complete]]*/

===== Further Reading =====

  * {{page>resources:Agile Software Development, Principles, Patterns, and Practices#reference}}
  * [[http://www.butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod|ButUncleBob: Principles of OOD]]
  * [[wiki>SingleResponsibilityPrinciple]]
  * [[wiki>OneResponsibilityRule]]
  * [[wiki>SeparationOfConcerns]]
  * [[wp>Separation of Concerns]]
  * [[http://blog.8thlight.com/cory-foy/2012/08/07/thinking-differently-about-srp.html|Thinking Differently About the Single Responsibility Principle]]
  * Coding Horror: [[http://blog.codinghorror.com/curlys-law-do-one-thing/|Curly's Law: Do One Thing]]

===== Discussion =====

Discuss this wiki article and the principle on the corresponding [[talk:principles:Single Responsibility Principle|talk page]].