<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">I think that is a little confusing and has potential to be ‘abused’. I think it’s more confusing that a `for(;;)` loop for instance, and that got removed. I think var + AnyIterator is more explicit, and can become the canonical way to do this.</div><div class=""><br class=""></div><div class="">Hopefully AnyIterator can be optimized to the same performance.</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On 20 May 2016, at 10:57 AM, Erica Sadun via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">On May 19, 2016, at 6:52 PM, Kevin Ballard via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><div class="">After having given this some thought, it seems apparent that `sequence(state:next:)` is equivalent to `AnyIterator({ ... })` where the closure captures a single mutable variable. The microbenchmark performance may differ slightly, as the AnyIterator version will allocate a box on the heap to hold the captured variable (assuming it can't get inlined entirely), whereas UnfoldSequence won't. But the functionality is the same.<br class=""></div><div class=""> </div><div class="">Thus the question: do we want to keep `sequence(state:next:)` or is it too close to AnyIterator in functionality? Arguments in favor of `sequence(state:next:)`:<br class=""></div><div class=""> </div><div class="">* It's equivalent to unfold and the dual of reduce, so people who've used functional programming languages may expect it to exist.<br class=""></div><div class="">* It allows you to create ad-hoc stateful sequences without polluting the current scope with a variable that exists solely to be captured.<br class=""></div><div class="">* If the cost of a small heap allocation is significant for your code, it may be more performant than AnyIterator.<br class=""></div><div class=""> </div><div class="">Personally, the most important reason here for me is not having to pollute the current closure with a variable. And this could actually be solved another way, by allowing the use of `var` in a capture list, which would let you say something like `AnyGenerator({ [var state=foo] in ... })`.<br class=""></div><div class=""> </div><div class="">Given all this, at this point I'm actually leaning towards saying`sequence(state:next:)` doesn't pull its own weight and we should just go with `sequence(initial:next:)`.<br class=""></div><div class=""> </div><div class="">-Kevin Ballard</div></div></div></blockquote><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Adding on, to the best of my understanding the biggest win in the stateful variation is to be able to create a sequence from a starting state without declaring any external variables, as in the perfectly wrong and evil example I showed Kevin:</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">enum</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Finger:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">case</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Thumb =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">1</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, Pointer, Middle, Ring, Pinky }</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo; min-height: 21px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);"><span class="" style="font-variant-ligatures: no-common-ligatures;">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Finger</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">static</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>members() -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">AnySequence</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Finger</span><span class="" style="font-variant-ligatures: no-common-ligatures;">> {</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">sequence</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">Thumb</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">rawValue</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, next: {</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> (</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">inout</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>idx:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">in</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">defer</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{ idx +=<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">1</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>}</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Finger</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(rawValue: idx)</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> })</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo; min-height: 21px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 15px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">for</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>finger<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">in</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Finger</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">members</span><span class="" style="font-variant-ligatures: no-common-ligatures;">() {<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(61, 29, 129);">print</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(finger) }</span></div></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">-- E</div><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; 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