Linux C style guide has this summarized pretty well:
"The maximum length of a function is inversely proportional to the complexity and indentation level of that function. So, if you have a conceptually simple function that is just one long (but simple) case-statement, where you have to do lots of small things for a lot of different cases, it’s OK to have a longer function.
However, if you have a complex function, and you suspect that a less-than-gifted first-year high-school student might not even understand what the function is all about, you should adhere to the maximum limits all the more closely."
"Less-than-gifted first-year student" is btw a great bar for the conceptual complexity. Another one I've seen elsewhere is "An SRE not familiar with the code woken up at 3 AM to troubleshoot an outage".
What really matters is "can I understand what this function roughly does at a glance?" In general, "length of function" is a reasonably-ish proxy for it, but as your quote says, sometimes longer is okay, and sometimes there are also other factors than just "length of function".
Either way, the question you should be asking during review is "can I understand this function?" and not "how long is this function?"
Unfortunately I think that cyclomatic complexity is a rough measure of this. It’s an attempt at an objective measurement, but I’ve never found it to be a particularly good one.
"The maximum length of a function is inversely proportional to the complexity and indentation level of that function. So, if you have a conceptually simple function that is just one long (but simple) case-statement, where you have to do lots of small things for a lot of different cases, it’s OK to have a longer function.
However, if you have a complex function, and you suspect that a less-than-gifted first-year high-school student might not even understand what the function is all about, you should adhere to the maximum limits all the more closely."
"Less-than-gifted first-year student" is btw a great bar for the conceptual complexity. Another one I've seen elsewhere is "An SRE not familiar with the code woken up at 3 AM to troubleshoot an outage".