Suppose that I am developing a relatively large project. I have already documented all my classes and functions with Doxygen, however, I had an idea to put a "programmer's notes" on each source code file.

The idea behind this is to explain in layman's terms how a specific class works (and not only why as most comments do). In other words, to give fellow programmers an other-view of how a class works.

For example:

 * As stated in the documentation, the GamepadManager class 
 * reads joystick joystick input using SDL and 'parses' SDL events to
 * Qt signals.
 * Most of the code here is about goofing around the joystick mappings.
 * We want to avoid having different joystick behaviours between
 * operating systems to have a more integrated user experience, since
 * we don't want team members to have a bad surprise while
 * driving their robots with different laptops.
 * Unfortunately, we cannot use SDL's GamepadAPI because the robots
 * are interested in getting the button/axes numbers, not the "A" or
 * "X" button.
 * To get around this issue, we created a INI file for the most common 
 * controllers that maps each joystick button/axis to the "standard" 
 * buttons and axes used by most teams. 
 * We choose to use INI files because we can safely use QSettings
 * to read its values and we don't have to worry about having to use
 * third-party tools to read other formats.

Would this be a good way to make a large project easier for new programmers/contributors to understand how it works? Aside from maintaining a consistent coding style and 'standard' directory organization, are there any 'standards' or recommendations for these cases?

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    Hell no. If your code is unreadable, documentation won't help. – Telastyn Aug 1 '15 at 0:29
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    @jeffo - the problem is that taking the time to do this can happen once. The time to keep code readable happens over time. I've been at places with this sort of documentation, done when the project was young, or when Joe the Perfectionist was still on the team. It then got abandoned and the comments lingered on, no longer accurate. – Telastyn Aug 1 '15 at 3:11
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    At a higher level at least, an out-of-code prose description of what a project does, how it works, and what tradeoffs have been made in the architecture is invaluable. This sort of a document is a must-read for a newcomer before they take a code tour. There is a lot of my-methodology-is-too-radical-for-docs-dude bullshit around the net, and while it is true that an initial arch doc and an evolving arch doc won't align, a prose description is necessary for anyone to quickly grasp a large, non-trivial codebase. Here is a (poor) example: zxq9.com/erlmud/html/001-002_architecture.html – zxq9 Aug 1 '15 at 8:51
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    @Telastyn: This has nothing to do with whether the code is readable or not (and I hope it is). Documenting design rationale is absolutely important. – Lightness Races in Orbit Aug 1 '15 at 15:01
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    @Telastyn: Yeah, maybe. Personally I'd write it in a standalone doc. But comment blocks at the top of source files isn't so bad. – Lightness Races in Orbit Aug 1 '15 at 15:48

10 Answers 10


This is awesome. I wish more software developers took the time and effort to do this. It:

  • States in plain English what the class does (i.e. it's responsibility),
  • Provides useful supplementary information about the code without repeating verbatim what the code already says,
  • Outlines some of the design decisions and why they were made, and
  • Highlights some of the gotchas that might befall the next person reading your code.

Alas, many programmers fall into the camp of "if code is written properly, it shouldn't have to be documented." Not true. There are many implied relationships between code classes, methods, modules and other artifacts that are not obvious from just reading the code itself.

An experienced coder can carefully craft a design having clear, easily-understandable architecture that is obvious without documentation. But how many programs like that have you actually seen?

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    And why the "Mythical Man Month" becomes a self-fulfilling prophecy, no one took the time to write all this out for the new dev when it was fresh on their mind and the project didn't fall behind. – JeffO Aug 1 '15 at 1:34
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    I agree with every point you make here. I don't like the term the OP used in his post how a class works. This changes with time and maintenance. Though my team does not put the above in the source. We maintain a wiki with decisions and copy the slack channel discussion about design decisions raw into a document (We provide a link from the decision summary and conclusion to the raw notes so we don't have to re-hash old decisions). All done neatly in github (so it is all in one place). – Martin York Aug 2 '15 at 0:07
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    My only issue is applying this globally. This class is complex enough, with certain gotchas available, clearly it's really useful (although you still end up dealing with Comment Rot). When a class is more obvious, the comment can be a bit superfluous. – deworde Aug 3 '15 at 10:53
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    "An experienced coder can carefully craft a design having clear, easily-understandable architecture that is obvious without documentation. But how many programs like that have you actually seen" While this is true, the quality of the documentation is never better than the quality of the code. Well architected code tends to have good, if pointless, documentation. Poorly architected code has comments like "increment x by 1" – deworde Aug 3 '15 at 15:12
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    I absolutely agree with this answer, and if I found something like the OP's example in code I would just be so happy. Just a single addition: consider adding a date to your comment, just to give an hint to eventual readers as to the freshness of the description, and update it every time you update the text. – Svalorzen Aug 4 '15 at 8:38

The key to working with a large codebase is not having to read the entire codebase to make a change. To enable a programmer to quickly find the code he is looking for, code should be organized, and the organization apparent. That is, each logical unit in the code, from the executable, the library, the namespace, down to the individual class should have a clearly apparent responsibility. I would therefore not just document source files, but also the directories they reside in.

Your programmer's notes also give background on design decisions. While this can be valuable information, I would separate it from the statement of responsibility (to enable the reader to choose whether he wants to read about the responsibility of the class or its design rationale), and move it as close to the source it describes as possible, to maximize the chance the documentation is updated when the code is (documentation is only useful if we can trust in its accuracy - outdated documentation can be worse than none!).

That said, documentation should remain DRY, i.e. not repeat information that could have been expressed in code or was already described elsewhere (phrases like "as the documentation states" are a warning sign). In particular, future maintainers will be just a proficient in the project's programming language as they are in English; paraphrasing the implementation in comments (which I see altogether too often when people are proud of their documentation) has no benefit, and is likely to diverge from the implementation, in particular if the documentation is not near the code it describes.

Finally, the structure of documentation should be standardized across the project so everyone can find it (it's a royal mess of Peter documents in the bug tracker, Sue in the wiki, Alan in the readme, and John in the source code ...).

  • Your first sentence is exactly how I view this. Large codebases should be composed as a number of smaller components where a new programmer can reliably change one without endangering any of the others. – Jon Chesterfield Aug 2 '15 at 22:47
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    move it as close to the source it describes as possible, to maximize the chance the documentation is updated when the code is. This is valuable experience. – laike9m Aug 7 '15 at 5:38
  • DRY as a guideline for the documentation is a very good point! That automatically sets the focus right and forbids the famously obnoxious "// increment x by 1" comments. – Hans-Peter Störr Aug 10 '15 at 12:23

I would not agree this is a very good approach, mainly due to

  1. When you refactor your project, move methods around, the documentation breaks.

  2. If documentation is not properly updated, it will result in more confusion than help understanding the code.

If you have unit tests for each method/ integration tests for each module, it would be a self documentation more maintainable and easier to understand compared to code comments.

Yes, having a proper directory structure definitely going to help.

  • +1 for Tests being the best way to understand a code base. Unit tests, integration tests, acceptance tests all tell the story about how the application is supposed to work, and how it's supposed to be used. – BZink Aug 6 '15 at 17:56

I'm personally a fan of a high-level design document - preferably written BEFORE any code - that gives an overview of the design and a list of classes and resources. A top-down design greatly simplifies things - yours might be "game engine -> hardware -> controllers -> joystick"; thus, a new programmer told "fix the 'a' button on the 'xyz controller" would at least know where to start looking.

Too many modern languages tend to break code into hundreds of tiny files, so just finding the correct file can be a challenge on even a moderate project.

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    20 years ago all my code was in one huge file. Now it is in thousands of small files and test files. There's a good reason for this and it reflects 20 years of software development (the general ecosystem, not my knowledge). Waaay too long for a comment though. – Michael Durrant Aug 1 '15 at 10:44
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    ah, the old waterfall method of writing a single, all encompassing, immutable, Truth before coding even starts and make it impossible to deviate in the implementation from said Truth. – jwenting Aug 2 '15 at 12:39
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    @jwenting: You don't have to take it that far. But it's still good to have some idea what you are building. – Robert Harvey Aug 3 '15 at 2:04
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    Certainly without the caveat of how to properly break this down and where to break the rules, you're going to very quickly have a document that's either out of date or a millstone. "I need to add a new class; to Documanto, the Behemoth that eats time!" – deworde Aug 3 '15 at 9:49
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    @deworde: I read that as "too lazy to maintain documentation." – Robert Harvey Aug 3 '15 at 14:16

If the code base is large - I try to provide a design document that maps out the key elements of its design and the implementation. The intention here is not to detail any of the classes used, but provide a key to code and the thought that went into the design. It gives a overarching context to the system, its components and the application thereof.

Things to include in the design document are;

  • Application architecture
  • Logical code structure
  • Data flows
  • Key patterns used and the motivation behind their use
  • Code source structure
  • How to build it (this offers insight into implicit dependencies and physical code source structure)

Following on from this, documentation for the classes, and functions/methods should be completed as appropriate. In particular the public API; it should be clear what the following all are in each case;

  • Preconditions
  • Effects
  • Invariants
  • Exception conditions (throws)
  • +1 Better than describing each class, as that will get out of date way faster than an overall design. – Lode Aug 10 '15 at 18:21

The most important rule I have found for making it easier for new developers to understand a codebase is perfect agreement is expensive.

If new developers must perfectly understand the system they are working on, it prevents all opportunities for on the job learning. I think the programmer's notes are an excellent start, but I would go further. Try to write code that, if approached anew, would allow a developer to figure out what they are doing on the fly, rather than requiring them to learn before they do. Little things like asserts for cases you know can never occur, along with comments explaining why the assert is valid, go a long way. So does writing code which fails gracefully rather than segfaulting if you do anything wrong.

  • My rule is that comments should be about WHY, not HOW. The code describes HOW. – user11393 Aug 4 '15 at 16:41

I have seen large classes with documentation, and after reading the documentation I haven't got a clue what this class is supposed to be good for and why anyone would use it! And at the same time, I had a need for some functionality and I was absolutely sure there must be a class to handle it, and couldn't find it anywhere - because there was no documentation that led me from what I needed to the class doing it.

So the first thing that I would want in the documentation is just a few sentences what a class does, and why I would want to use it. The comments in the original question are doing quite well in that respect. After reading these comments, if I had a joystick that doesn't work well because I can't interpret the values it delivers, I would know what code to check.


Similar to what @meriton said, break the code down into separate components. Even better, break down the codebase into separate packages (JARs, gems, eggs, whatever) to make it even more clear how the components are separated. If there is a bug, a developer only needs to find the package where the bug is, and (hopefully) only fix it there. Not to mention, it's easier to do unit testing, and you get to take advantage of dependency management.

Another solution: make the codebase smaller. The less code there is, the easier it is to understand. Refactor out unused or duplicated code. Use declarative programming techniques. This takes effort, of course, and often isn't possible or practical. But it's a worthy goal. As Jeff Atwood has written: The Best Code Is No Code At All


For complex systems it may be worth it to not just document each file, but their interactions and hierarchy, and how the program structures and why.

For example a game engine is usually quite complex and its hard to decide what calls what after hundred layers of abstraction. It may be worth creating a file like "Architecture.txt" to explain how and why is the code structured like this, and why there is that pointless looking abstraction layer there.


This can be partly because it is hard for a single programmer to write it, as each individual understands only their part of project.

Sometimes you can get this info from the notes of the project manager , but that is all you will get, as they will rarely rewrite their notes in this format.

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    If you look at github you'll find a lot of projects that have this kind of note in a README.md file. It's become so much a part of the culture of git in general and javascript projects in particular to most people won't use a library that does not have this sort of high level documentation. So it's untrue that "no programmer would write it" since you only need to look at something like jQuery or socket.io and find programmers who write such things. It has also become a culture that README files that are not accurate generate bug reports. – slebetman Aug 1 '15 at 9:41
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    This doesn't seem to answer the question, which was looking for reasons why the documentation style proposed would or wouldn't work, and also for documentation standards. – user52889 Aug 1 '15 at 10:57
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    If you have a team of programmers working on a product, and each programmer only understands the specific code that they worked on, then not only is your team incredibly dysfunctional with an absurd bus factor, but one questions the quality of the code. How does one integrate code into a product without understanding the rest of the code in the same system??!? – Lightness Races in Orbit Aug 1 '15 at 15:03

protected by gnat Aug 2 '15 at 12:54

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