Here's a quick compilation of the good and bad of coding, as discovered by actual practitioners over many years. This might be a springboard for a series of technical overviews, where we go both broad and deep, having fun while learning new things.
Clean Code (Good)
- 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 root cause. Always look for the root cause of a problem.
- Keep configurable data at high levels.
- Prefer polymorphism to if/else or switch/case.
- Separate multi-threading code.
- Prevent over-configurability.
- Use dependency injection.
- Follow Law of Demeter. A class should know only its direct dependencies.
- 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 primitive type.
- Avoid logical dependency. Don't write methods which works correctly depending on something else in the same class.
- Avoid negative conditionals.
- Choose descriptive and unambiguous names.
- Make meaningful distinction.
- Use pronounceable names.
- Use searchable names.
- Replace magic numbers with named constants.
- Avoid encodings. Don't append prefixes or type information.
- Do one thing.
- Use descriptive names.
- Prefer fewer arguments.
- Have no side effects.
- Don't use flag arguments. Split method into several independent methods that can be called from the client without the flag.
- 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 explanation of intent.
- Use as clarification of code.
- Use as 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 close.
- 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.
- One assert per test.
Code smells from Clean Code (Perhaps Bad)
- 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 involved risks and high effort.
- Needless Complexity.
- Needless Repetition.
- Opacity. The code is hard to understand.
List of Code Smells From Wikipedia
- Mysterious Name: functions, modules, variables or classes that are named in a way that does not communicate what they do or how to use them.
- Duplicated code: identical or very similar code that exists in more than one location.
- Contrived complexity: forced usage of overcomplicated design patterns where simpler design patterns would suffice.
- Shotgun surgery: a single change that needs to be applied to multiple classes at the same time.
- Uncontrolled side effects: side effects of coding that commonly cause runtime exceptions, with unit tests unable to capture the exact cause of the problem
- Variable mutations: mutations that vary widely enough that refactoring the code becomes increasingly difficult, due to the actual value's status as unpredictable and hard to reason about.
- Boolean blindness: easy to assert on the opposite value and still type checks.
- Large class: a class that has grown too large. See God object.
- Feature envy: a class that uses methods of another class excessively.
- Inappropriate intimacy: a class that has dependencies on implementation details of another class. See Object orgy.
- Refused bequest: a class that overrides a method of a base class in such a way that the contract of the base class is not honored by the derived class. See Liskov substitution principle.
- Lazy class/freeloader: a class that does too little.
- Excessive use of literals: these should be coded as named constants, to improve readability and to avoid programming errors. Additionally, literals can and should be externalized into resource files/scripts, or other data stores such as databases where possible, to facilitate localization of software if it is intended to be deployed in different regions.
- Cyclomatic complexity: too many branches or loops; this may indicate a function needs to be broken up into smaller functions, or that it has potential for simplification/refactoring.
- Downcasting: a type cast which breaks the abstraction model; the abstraction may have to be refactored or eliminated.
- Orphan variable or constant class: a class that typically has a collection of constants which belong elsewhere where those constants should be owned by one of the other member classes.
- Data clump: Occurs when a group of variables are passed around together in various parts of the program. In general, this suggests that it would be more appropriate to formally group the different variables together into a single object, and pass around only the new object instead.
- Too many parameters: a long list of parameters is hard to read, and makes calling and testing the function complicated. It may indicate that the purpose of the function is ill-conceived and that the code should be refactored so responsibility is assigned in a more clean-cut way.
- Long method: a method, function, or procedure that has grown too large.
- Excessively long identifiers: in particular, the use of naming conventions to provide disambiguation that should be implicit in the software architecture.
- Excessively short identifiers: the name of a variable should reflect its function unless the function is obvious.
- Excessive return of data: a function or method that returns more than what each of its callers needs.
- Excessive comments: a class, function or method has irrelevant or trivial comments. A comment on an attribute setter/getter is a good example.
- Excessively long line of code (or God Line): A line of code which is too long, making the code difficult to read, understand, debug, refactor, or even identify possibilities of software reuse.