Coupling

Required

• Talk only to your direct neighbours

  Required

  A function calls methods on its own object, its arguments and the objects it creates. It never reaches through one object to steer another, as in a.getB().getC().doSomething().

• Make the order of calls impossible to get wrong

  Required

  If methods must run in a set order, the code must enforce it. Never rely on callers remembering to call init() first.

• Pass state in instead of sharing globals

  Required

  Never share changeable data through globals, singletons or module-level variables when it changes how code behaves. Pass state in, and return new state out.

Recommended

• Tell objects what to do

  Recommended

  Give an object a command instead of reading its state and deciding for it. The rule that uses the data lives next to the data.

• Keep internals private

  Recommended

  Each module exports only what its callers need. Everything else stays private, so it can change without breaking anyone.