Rules of writing clean code

Writing clean code is a virtue of a software engineer. We should write the code in a way that others can easily understand and reuse. The following are some rules for writing clean code:

General rules

  • Follow standard conventions.
  • Keep it simple stupid. Simpler is always better. Reduce complexity as much as possible.
  • Boy scout rule. Leave the campground cleaner than you found it.
  • Always find the root cause and always look for the root cause of a problem.

Design rules

  • Keep configurable data at high levels.
  • Prefer polymorphism to if/else or switch/case.
  • Separate multi-threading code.
  • Prevent too much configuration.
  • Use dependency injection.
  • Follow the Law of Demeter. A class should know only its direct dependencies.

Understandability tips

  • Be consistent. If you do something a certain way, do all similar things in the same way.
  • Use explanatory variables.
  • Encapsulate boundary conditions. Boundary conditions are hard to keep track of. Put the processing for them in one place.
  • Prefer dedicated value objects to a primitive type.
  • Avoid logical dependency. Don’t write methods that work correctly depending on something else in the same class.
  • Avoid negative conditionals.

Names rules

  • Choose descriptive and unambiguous names.
  • Make a meaningful distinction.
  • Use pronounceable names.
  • Use searchable names.
  • Replace magic numbers with named constants.
  • Avoid encodings. Don’t append prefixes or type information.

Functions rules

  • Keep the function small.
  • Do one thing.
  • Use descriptive names.
  • Prefer fewer arguments.
  • Have no side effects.
  • Don’t use flag arguments and split the method into several independent methods that can be called from the client without the flag.

Comments rules

  • Always try to explain yourself in code.
  • Don’t be redundant.
  • Don’t add obvious noise.
  • Don’t use closing brace comments.
  • Don’t comment out code. Just remove.
  • Use as an explanation of intent.
  • Use as clarification of code.
  • Use as a warning of consequences.

Source code structure

  • Separate concepts vertically.
  • Related code should appear vertically dense.
  • Declare variables close to their usage.
  • Dependent functions should be closed.
  • Similar functions should be close.
  • Place functions in the downward direction.
  • Keep lines short.
  • Don’t use horizontal alignment.
  • Use white space to associate related things and disassociate weakly related.
  • Don’t break indentation.

Objects and data structures

  • Hide internal structure.
  • Prefer data structures.
  • Avoid hybrids structures (half object and half data).
  • Should be small.
  • Do one thing.
  • Small number of instance variables.
  • Base class should know nothing about their derivatives.
  • Better to have many functions than to pass some code into a function to select a behavior.
  • Prefer non-static methods to static methods.

Rules for writing Tests

  • One assert per test.
  • Readable.
  • Fast.
  • Independent.
  • Repeatable.

Code smells

  • Rigidity. The software is difficult to change. A small change causes a cascade of subsequent changes.
  • Fragility. The software breaks in many places due to a single change.
  • Immobility. You cannot reuse parts of the code in other projects because of the involved risks and high effort.
  • Needless Complexity.
  • Needless Repetition.
  • Opacity. The code is hard to understand.