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Summary of 'Clean code' by Robert C. Martin

Code is clean if it can be understood easily – by everyone on the team. Clean code can be read and enhanced by a developer other than its original author. With understandability comes readability, changeability, extensibility and maintainability.

General rules

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

Design rules

  1. Keep configurable data at high levels.
  2. Prefer polymorphism to if/else or switch/case.
  3. Separate multi-threading code.
  4. Prevent over-configurability.
  5. Use dependency injection.
  6. Follow Law of Demeter. A class should know only its direct dependencies.

Understandability tips

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

Names rules

  1. Choose descriptive and unambiguous names.
  2. Make meaningful distinction.
  3. Use pronounceable names.
  4. Use searchable names.
  5. Replace magic numbers with named constants.
  6. Avoid encodings. Don't append prefixes or type information.

Functions rules

  1. Small.
  2. Do one thing.
  3. Use descriptive names.
  4. Prefer fewer arguments.
  5. Have no side effects.
  6. Don't use flag arguments. Split method into several independent methods that can be called from the client without the flag.

Comments rules

  1. Always try to explain yourself in code.
  2. Don't be redundant.
  3. Don't add obvious noise.
  4. Don't use closing brace comments.
  5. Don't comment out code. Just remove.
  6. Use as explanation of intent.
  7. Use as clarification of code.
  8. Use as warning of consequences.

Source code structure

  1. Separate concepts vertically.
  2. Related code should appear vertically dense.
  3. Declare variables close to their usage.
  4. Dependent functions should be close.
  5. Similar functions should be close.
  6. Place functions in the downward direction.
  7. Keep lines short.
  8. Don't use horizontal alignment.
  9. Use white space to associate related things and disassociate weakly related.
  10. Don't break indentation.

Objects and data structures

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


  1. One assert per test.
  2. Readable.
  3. Fast.
  4. Independent.
  5. Repeatable.

Code smells

  1. Rigidity. The software is difficult to change. A small change causes a cascade of subsequent changes.
  2. Fragility. The software breaks in many places due to a single change.
  3. Immobility. You cannot reuse parts of the code in other projects because of involved risks and high effort.
  4. Needless Complexity.
  5. Needless Repetition.
  6. Opacity. The code is hard to understand.
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I am not a programmer myself. So, I haven't read the book myself (although I knew about it for sure 😉) and I read the summary here now for the first time—and I just realized, the recommendations actually apply to quite a lot of other things as well!

So, for all non-engineers, it's worth the read! 💡 Thanks for sharing. 👍

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I would like to contribute to this amazing Clean Code hints by one that I noticed it's possible to be done and nobody talks about...

Conditional Simplification

You can always turn a complex conditional into a simpler one through the Propositional Logic rules
Screen Shot 2021-11-16 at 21 27 24

  • References
  1. De Morgan
  2. Tautology
  3. Propositional Logic

Inspired by Robert C Marin's book: Clean Code

Or you could just paste an "obfuscated" ((a && b) || (b &&c) || (!a && !c)) version of your condition into and let it do the work. (Minimal forms)

That's work. But if "setting" is null when hideOnGrid is false, it's generate exception.

You could define additional vars to add semantic. Ex.

const mustHideOnGridByColumn = column.hideOnGrid;
const mustHideOnGridBySetting = setting && setting.hide_on_grid;

return !(mustHideOnGridByColumn || mustHideOnGridBySetting);
 // or: return !mustHideOnGridByColumn && !mustHideOnGridBySetting

This way is very clean and improves readability

This is by far one of the best things I’ve started doing for a while.

Usually boolean conditions are a representation of a behavior, meaningful names will always help your code read like a story.

That way just by reading the variable name you get the problem statement.

For example:

if (isReadyToReceiveMessage) {…}

Of course one should be careful to not create misleading variables that don’t mean what the condition represent. (tests help with that semantics).

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Victorcorcos commented Sep 12, 2023

@Victorcorcos if setting is null or undefined the old code is working but not the new code, or am I missing something ?

The new code will work, because this is applied:

  1. Avoid NPE on q by using || {}
  • Before
setting = fieldSettings[column.foreignAttribute] || fieldSettings[column.description]
  • After
setting = fieldSettings[column.foreignAttribute] || fieldSettings[column.description] || {}

So, in case setting is null/undefined, it will be {}, which won't cause NPE.

→ We can't see that on the picture, but that || {} was the change on that specific line

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Can I download this book somewhere for free? TY<3

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thanks for this @wojteklu 👍

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it helps a lot for me thank you.

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sounds great, thank you!

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jjsutil commented May 4, 2024

Thanks for this notes!

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Would be helpful if someone will add code example refactored as above one.

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