Writing good comments is an art form, and beginner programmers often struggle with it. They know comments mostly from their text books, where the comments explain what is happening to someone who doesn’t yet know programming, and nobody has told them yet that that is not at all a useful commenting style outside of education. So that’s how they use them. It usually ends up making the code harder to read, not easier.
Later on, programmers will need to learn a few rules about comments, like:
Assume that whoever reads your code knows the programming language, the platform and the problem domain at least in general terms. You are not writing a teaching aid, you are writing presumably useful software.
Don’t comment the obvious. (Aside from documentation comments for function/method/class signatures)
Don’t comment what a line is doing. Instead, write your code, especially names for variables, constants, classes, functions, methods and so on, so that they produce talking code that needs no comments. Reserve the “what” style comments for where that just isn’t possible.
Do comment the why. Tell the reader about your intentions and about big-picture issues. If an if-statement is hard to parse, write a corresponding if clause in plain English on top of it.
In some cases, comment the “why not”, to keep maintenance programmers from falling in the same trap you already found.
I would argue that if an if statement is hard to parse, replace the entire condition with simpler to read (but way more specific) variables that you assign values (the original condition expression) in the line above. No need for comments in that case
Comments should be part of code review, having at least two pairs of eyes on comments is crucial. Something that’s obvious to one person maybe isn’t so obvious to another. Writing good comments is as hard or harder than writing good code, so having it checked for mistakes and quality is a must
Comments aren’t the actual documentation and aren’t a reason not to write documentation to go along with your code. Often I see larger projects where each class and function is documented in comments, but the big picture and the how and why of the overall structure is completely missing. Remember that in the real world you often have a lot of folk that need to understand how the code works, who aren’t programmers themselves. They can’t read the code or don’t have access to the code. Writing documentation is still important.
Please for the love of god when you change code, check if the comments need to be updated as well. Not just around the immediate area, but also the entire file/class and related files. I’ve worked on large codebases before with a high wtf factor and having the code do something different to or even opposite the comments is a nightmare. I’d rather have no comments than wrong comments.
This is a notoriously bad book. If you read the part about comments (which I don’t know about, and am willing to accept is good) make sure to skip everything else because Robert Martin is a fraud.
Don’t comment what a line is doing. Instead, write your code, especially names for variables, constants, classes, functions, methods and so on, so that they produce talking code that needs no comments.
Over and over and over again in my experience this just doesn’t work. Readable code does not substitute for comments about what the code should be doing.
In this day and age of source control I don’t think this is fully necessary. If you want to know the why, you can look into the commit history and see which ticket is connected to it. There you might even see the discussions around the ticket as well. But this requires good source control discipline.
Why not put the “why” in a comment and save people the job of dredging through old commits and tickets to figure out what the code is for? I’d thank someone for saving me the hassle.
Going back to the original ticket can offer far more info than what any “why” comment can give. You can see how old it is, if there are any connected tickets, who were involved with it, step by step instructions how to reproduce the bug, etc.
In any modern IDE “dredging through old commits” means clicking a single button to see who last changed the line. From there it often makes sense to go look at the PR to see a higher level of what was changed. You cannot include all of that context in a single comment.
Writing good comments is an art form, and beginner programmers often struggle with it. They know comments mostly from their text books, where the comments explain what is happening to someone who doesn’t yet know programming, and nobody has told them yet that that is not at all a useful commenting style outside of education. So that’s how they use them. It usually ends up making the code harder to read, not easier.
Later on, programmers will need to learn a few rules about comments, like:
Commenting the why not is key. Half my comments are explaining why I had to use this hack as a warning that the obvious fix doesn’t work!
I would argue that if an if statement is hard to parse, replace the entire condition with simpler to read (but way more specific) variables that you assign values (the original condition expression) in the line above. No need for comments in that case
Good advice, just to add to this:
This is a notoriously bad book. If you read the part about comments (which I don’t know about, and am willing to accept is good) make sure to skip everything else because Robert Martin is a fraud.
Agreed, removed
I’ve seen cases of outdated comments in the same line of code it’s describing. People suck at maintaining comments.
Over and over and over again in my experience this just doesn’t work. Readable code does not substitute for comments about what the code should be doing.
In this day and age of source control I don’t think this is fully necessary. If you want to know the why, you can look into the commit history and see which ticket is connected to it. There you might even see the discussions around the ticket as well. But this requires good source control discipline.
It has helped me many times.
Why not put the “why” in a comment and save people the job of dredging through old commits and tickets to figure out what the code is for? I’d thank someone for saving me the hassle.
You can also do that if you think it’s useful.
Going back to the original ticket can offer far more info than what any “why” comment can give. You can see how old it is, if there are any connected tickets, who were involved with it, step by step instructions how to reproduce the bug, etc.
In any modern IDE “dredging through old commits” means clicking a single button to see who last changed the line. From there it often makes sense to go look at the PR to see a higher level of what was changed. You cannot include all of that context in a single comment.