Ask HN: How do you deal with 2000 line functions?

Go to the part that you suspect you need to modify, identify a block of code that together forms something you can give a name, i.e. "initialize_doodad_struct", "validate_widget_params", pull it out put it in a function. Now look at all identifiers that are referenced or declared in your block of code, do a ack or ctrl+f through the 2000-N line function to 100% verify that they're not referenced anywhere. If they aren't you can safely encapsulate them in your new function (if you're working in a static language you probably could just right-mouse-click-extract to do all this).

Then immediately verify that the code still works. Run it, ideally in unit tests but most certainly also in real world(-like) scenarios. Do this for every small step. If your codebase takes 2 hours to compile, instead make a commit. Make a commit for every single 3-10 line extraction you do. (do it anyway, it'll look good and everyone will love you)

And then repeat until either the part you wanted to modify is clear to you, or there's nothing more to extract ;)

By the way, I'm a Ruby programmer mainly, and in Ruby any function over 10 lines is frowned upon. I know that in some programming language communities (looking at you C and C++!) a 200 line function doesn't raise any eyebrows, and they'll sometimes even scold you for extracting a function if it doesn't 'add' anything. I think this is because in C every function pollutes the global namespace, so there's a little more cost associated with it.

getting a feel for the structure of the function helps me understand it.

Ex:

function someFunction () {

    if () {
        for () {
            if () {

            } else {

            }
        }

        if () {
            for () {
            
            }
        }
    }

}