At one point I was working on a utility to detect suboptimal sequence of method calls; canonical example is using "[1,2,3].select {|x| x > 1 }.first" rather tha

At one point I was working on a utility to detect suboptimal sequence of method calls; canonical example is using "[1,2,3].select {|x| x > 1 }.first" rather than "[1,2,3].detect {|x| x > 1}". These can be performance issues, although the bigger win is in readability and communicating the developer intent. More details and examples here if you're interested: https://thomasleecopeland.com/2014/10/22/finding-suboptimal-api-usage.html https://thomasleecopeland.com/2014/10/22/finding-suboptimal-... I haven't worked on it much recently though because the problems it found weren't that significant. But I like the idea of runtime analysis for finding issues, especially in a dynamically-typed language.