<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Running this on my MBP with 10 as the parameter: <a href="https://gist.github.com/zneak/ae33bb970a08632cfb2925e2049f9e7a" class="">https://gist.github.com/zneak/ae33bb970a08632cfb2925e2049f9e7a</a> <div class=""><br class=""></div><div class="">I get a runtime of about 10 seconds, 45% of which is spent in retain/release calls according to Instruments (!!), and at least half of that from Expr.count. Looking at the IR, Swift generously sprinkles retain/release calls through the outlined copy method:</div><div class=""><br class=""></div><div class=""><ul class="MailOutline"><li class="">`self` is retained at the beginning of `count`</li><li class="">The values that you get out of destructuring are retained</li><ul class=""><li class="">Of course, when you get `count` on these, they are retained again</li></ul></ul></div><div class=""><br class=""></div><div class="">Of course, Expr.count cannot modify itself or its subexpressions because the functions are not mutating; in fact, no function in that program can mutate an enum case. Why, then, is Swift retaining/releasing `self` and the values obtained from destructured patterns? They can't go away. Shouldn't we be getting guaranteed references instead of owning references?</div><div class=""><br class=""></div><div class="">That seems to hit pattern-matching-heavy programs with indirect cases pretty hard, and it's pretty frustrating because that seems to be about the nicest way to write this program, and there's no workaround from the developer's perspective. I don't think that this is a fatal flaw of refcounting, but unless I'm missing something, that's sub-par behavior.</div><div class=""><br class=""></div><div class="">Félix</div></body></html>