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Comment by tshaddox | Hacker News Reader

I’m referring to competent engineers maintaining understanding over time of all the code they’ve produced. Long before agentic coding, codebases routinely grew beyond the comprehensive understanding of their own authors.

Of course less competent engineers (or anyone on a particularly disorganized or desperate day) can literally hand-write code they don’t understand even as they write it, but that’s not really what I’m talking about.

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As I said, you understand the part you're modifying because otherwise you wouldn't know how to modify it.

> literally hand-write code they don’t understand even as they write it

I find this literally impossible. How can you even start typing anything without knowing what to type?

There's understanding and there's understanding.

Have you never "fixed a bug", only to realize that you just papered over a single symptom, while the underlying bug is still intact?

People you're disagreeing with (I think!), would say that during your first attempt, you didn't _really_ understand the part you're modifying.

It is _very easy_ to do this in large codebases, and even more so when working on anything touching UI.

I suppose I am confused about why you’re confused. There’s a long history in computing of describing pieces of programming languages syntax syntax as “incantations” and similar. I suspect it has been very common, especially in the early part of developers’ careers, to know what you’re trying to do and to know that this code accomplishes it, but to not understand how the code works, to not be able to use the technique more generally, and to not understand all the effects your change has on the rest of the system.

I see, I guess I'm using "understanding" in the more literal sense of being able to put enough context together in your mind to type the characters on screen, not necessarily understand enough to know how it affects every other part of the codebase.

It's the style of understanding that says "if your animation is stuttering, set `gc.tune(pause_length=0, frequency=-1)`. Or "to make data access fast, remember to always use `integritychecks=omit;encryption=export-grade;checksum=md5`".

You don't know what these things do and what their effects really are (examples and syntax illustrative, but this is the kind of code that has disastrous effects when used carelessly), but you know they achieve your particular micro goal of "make things go fast" or "make this fit in packets on these strange industrial networks customer X has" or whatever.

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