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Single Responsibility Principle

  • “Every piece of code must have a single purpose to exist”
  • Encourages higher cohesion
  • Only keep things together if they really belong together
  • Don’t put multiple classes in a single file
  • Long methods are bad because
    • hard to read
    • hard to test
    • hard to reuse
    • leads to duplication
    • hard to maintain
    • tight coupling

Some quick notes based on Uncle Bob’s talk on SRP:

Things that change for the same reasons should be grouped together. e.g. If our software generates a report, and the view contains SQL queries, changes to the view could be initiated by the DBA or the person using that report.

Responsibilities should map with the person initiating the change to the module.

Isolate code such that changes requested by people who request one kind of change doesn’t impact code that affects people who request a different kind of change. Eg. Changes requested by an accountant should not impact modules that would be affected by changes required by a clerk who uses the generated reports.