[VladKovac]

Functional programmers love to emphasize how all the aspects of programming that their pet language is uniquely good at dealing with also happen to be the biggest problems in code maintenance. Is there any actual data on what the biggest problem sources are?

[swift]

I'd love more data on this too, but I do think it's worth pointing out that it's pretty uncontroversial that the more control flow paths you have, the harder your code is to reason about. That's the basic assumption of the notion of cyclomatic complexity, after all.