rails/rails — pull request #8443 by gbchaosmaster (2012-12-07 01:00:11+00:00)
Title: Use #flat_map instead of .map { foo }.flatten

I was discussing this matter on #ruby, and we eventually got curious as to whether or not it made any difference in performance- surprisingly, benchmarks showed that ```#flap_map``` was twice as fast as calling ```#map```, then ```#flatten``` on that result. Modern Ruby code should definitely be using this method.

With this PR there are, to my knowledge, no more occurrences of the old way of flattening a ```#map```.