![]() ![]() The reason it is important to keep a class focused on a single concern is that it makes the class more robust. It would be a bad design to couple two things that change for different reasons at different times. The single-responsibility principle says that these two aspects of the problem are really two separate responsibilities, and should, therefore, be in separate classes or modules. These two things change for different causes. Second, the format of the report could change. First, the content of the report could change. Imagine such a module can be changed for two reasons. rewritten).Īs an example, consider a module that compiles and prints a report. Martin defines a responsibility as a reason to change, and concludes that a class or module should have one, and only one, reason to be changed (e.g. In 2014 Martin published a blog post titled "The Single Responsibility Principle" with a goal to clarify what was meant by the phrase "reason for change." Example Martin described it as being based on the principle of cohesion, as described by Tom DeMarco in his book Structured Analysis and System Specification, and Meilir Page-Jones in The Practical Guide to Structured Systems Design. Martin in his article "The Principles of OOD" as part of his Principles of Object Oriented Design, made popular by his 2003 book Agile Software Development, Principles, Patterns, and Practices. Hence, each module should be responsible for each role. For example, while they might be the same person, the role of an accountant is different from a database administrator. Because of confusion around the word "reason" he has also clarified saying that the "principle is about people." In some of his talks, he also argues that the principle is, in particular, about roles or actors. ![]() Martin, the originator of the term, expresses the principle as, "A class should have only one reason to change". The single-responsibility principle ( SRP) is a computer programming principle that states that "A module should be responsible to one, and only one, actor." The term actor refers to a group (consisting of one or more stakeholders or users) that requires a change in the module. ![]()
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