It seems to be quite a long time since I've written a genuine "code" blog post. Time to fix that. This material may well be covered elsewhere – it's certainly not terrifically original, and I've been meaning to post about it for a long time. In particular, I remember mentioning it at CodeMash in 2012. Anyway, the time has now come. Refresher on array covariance Just as a bit of background before we delve into the performance aspect, let me remind you what array covariance is, and when it applies. The ba[...]