We have a wiki memo: https://cwiki.apache.org/confluence/display/DAFFODIL/Coding+for+Performance which is about coding style for things like daffodil runtimes, which have to go fast.
I added a section "Avoid Destructuring by Pattern in Assignments" which is a guidance that goes along with the guidance for avoiding match-case pattern matching in performance code. Interestingly, there's also a code coverage thing going on here. If you write val Some(x) = y Where y is Option[T], the CodeCov tool will always red line this statement as non-covered. This is because there is a type-conversion here. The scala compiler is checking the type here, and as that code path cannot happen (or you wouldn't have written this) there is uncovered code here. The code path that checks the type is ascribed to this statement in the code, and so you get a red-mark because that type check never fails in testing. I updated the memo to suggest writing `val x = y.get` instead, which first we know is going to generate best-possible byte-code, and second which will fix the codecov red line. Other guidelines suggest sticking with Maybe[T] instead of Option[T] in the runtime, but in some cases libraries are being called which utilize Option types so you may have no choice.
