DEV Community

Cover image for Clean Code Tip: Not all comments are bad
Davide Bellone
Davide Bellone

Posted on • Originally published at

Clean Code Tip: Not all comments are bad

Many developers say that

All comments are bad! πŸ’’

False! Most of the comments are bad!

Examples of bad comments

For example, look at this method, and look at the comments:

/// <summary> Checks if the password is valid </summary>
/// <param name="password">The password to be validated</param>
/// <returns>True if the password is valid, false otherwise</returns>
public bool IsPasswordValid(string password)
    Regex regex = new Regex(@"[a-z]{2,7}[1-9]{3,4}");
    var hasMatch = regex.IsMatch(password);
    return hasMatch;
Enter fullscreen mode Exit fullscreen mode

Here the comments are pointless - they just tell the same things you can infer by looking at the method signature: this method checks if the input string is a valid password.

So, yes, those kinds of comments are totally meaningless, and they should be avoided.

Good types of comments

But still, there are cases when writing comments is pretty helpful.

public bool IsPasswordValid(string password)
    // 2 to 7 lowercase chars followed by 3 or 4 numbers
    // Valid:   kejix173
    //          aoe193
    // Invalid: a92881
    Regex regex = new Regex(@"[a-z]{2,7}[1-9]{3,4}");
    return regex.IsMatch(password);
Enter fullscreen mode Exit fullscreen mode

Here the purpose of the comment is not to explain what the method does (it's already pretty explicit), but it explains with examples the Regular Expression used to validate the password. Another way to explain it is by adding tests that validate some input strings. In this way, you make sure that the documentation (aka the tests) is always aligned with the production code.

By the way, for more complex calculations, adding comments explaining WHY (and not HOW or WHAT) a piece of code does is a good way to help developers understand the code.

Another reason to add comments is to explain why a specific piece of code exists: examples are legal regulations, related work items, or references to where you've found that particular solution.


Always pay attention when writing comments: yes, they often just clutter the code. But they can really add value to the code, in some cases.

To read more about good and bad comments, here's a well-detailed article you might like:

πŸ”— Clean code tips - comments and formatting

Happy coding!


Top comments (1)

moopet profile image
Ben Sinclair

I know this is an example, but I'd say that IsPasswordValid isn't clear enough - if I saw that and didn't have context I'd assume it was part of the auth process. If I was reviewing this I'd change it to DoesPasswordHaveSufficientEntropy or something equally verbose that distinguishes it from DoesPasswordMatchWhatTheUserSetLastWeek.

The comments which may appear in a tooltip in your IDE along with the method signature might actually help in the case of a set of fresh eyes looking through your code, though they'd have to change to something else as well!

I think my confusion is from this being a class method, where the assumption is that this is some kind of "person" class which already knows about the user. Perhaps with that context as well it'd be more obvious.

In this example, the comments re-state the signature, but they could be used to add information for other developers without refactoring IsPasswordValid out of the class or renaming it and having to check it's not being referenced somewhere else in some other pending merge or something.