<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=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""></div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><blockquote type="cite" class="">On Nov 9, 2017, at 1:48 PM, Ben Cohen via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></blockquote><div class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Nov 9, 2017, at 10:45 AM, BJ Homer 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=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">On Nov 9, 2017, at 11:36 AM, Kevin Ballard via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><div class=""><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class="">
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<div class=""><div class="">On Wed, Nov 8, 2017, at 09:29 PM, Paul Cantrell via swift-evolution wrote:<br class=""></div>
<blockquote type="cite" class=""><div style="word-wrap:break-word;line-break:after-white-space;" class=""><div class=""><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px;font-stretch:normal;line-height:normal;background-color:rgb(255, 255, 255);" class=""><div class="">The problem in the Doodads example is that <b class="">the name <span class="colour" style="color:rgb(88, 126, 168)"><span class="font" style="font-family:Menlo"><span class="size" style="font-size:11px">flatMap</span></span></span> is used to identify two distinct intents</b>: concatenating arrays and filtering nils. One can argue that those two operations are, in some lofty abstract sense, if you squint, two instances of some more general pattern — but I don’t think it’s fair to say that they represent the same <i class="">intent</i>. These separate intents deserve separate names.<br class=""></div>
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<div class="">They absolutely represent the same intent if you think of an optional as a collection of zero or one elements.</div></div></div></blockquote></div></div></div></div></blockquote></div></div></div></blockquote><div class=""><br class=""></div><div class="">This is precisely the “lofty abstract sense, if you squint” to which I was referring. I stand by that characterization. Just because there is a clever isomorphism between two types doesn’t mean people use them with equivalent intent.</div><div class=""><br class=""></div><div class="">Splitting that hair aside, the point of that example code stands: using the same name for both flatMap variants causes the type checker to miss programmer errors it would otherwise catch. (And unlike the first motivating example in the proposal, the “warn on optional hoisting” feature would not help at all.)</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div dir="auto" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="">
</div></div></blockquote></div><div class="">But as `Optional` does not conform to collection, I would suggest that the vast majority of of developers do _not_ think of them as a collection of zero or one elements. (I certainly don’t know any who naturally think of it that way.) We don’t treat Optional as a collection anywhere else in the API, and it seems odd to do so in just this one case.</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">And, to be clear, the lack of Collection conformance by Optional is an active choice, not an omission.</div><div class=""><br class=""></div><div class="">The “think of optionals as collections” explanation is a good way to help people who are confused by the overload. But an even better way would be to not have a confusing overload in the first place.</div></div></div></div></blockquote></div><br class=""><div class="">Exactly so. A much crisper way of stating my sprawling argument.</div><div class=""><br class=""></div><div class="">I’m personally grateful that Swift reminds me that, for example, I need the question mark in <span style="font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">view.</span><span style="color: rgb(88, 126, 168); font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">gestureRecognizers</span><span style="font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">?.</span><span style="color: rgb(88, 126, 168); font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">count</span>. It would be maddening if <span style="font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">view.</span><span style="color: rgb(88, 126, 168); font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">gestureRecognizers</span><span style="font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">.</span><span style="color: rgb(88, 126, 168); font-family: Menlo; font-size: 11px; background-color: rgb(255, 255, 255);" class="">count</span> compiled, and always returned either 0 or 1. Imagine it!</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(88, 126, 168); background-color: rgb(255, 255, 255);" class=""><span style="color: #000000" class=""> view.</span>gestureRecognizers<span style="color: #000000" class="">.</span>count<span style="color: #000000" class=""> </span><span style="color: #668b49" class="">// returns 0</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(88, 126, 168); background-color: rgb(255, 255, 255);" class=""><span style="color: #000000" class=""> view.</span>gestureRecognizers<span style="color: #000000" class=""> = []</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(88, 126, 168); background-color: rgb(255, 255, 255);" class=""><span style="color: #000000" class=""> view.</span>gestureRecognizers<span style="color: #000000" class="">.</span>count<span style="color: #000000" class=""> </span><span style="color: #668b49" class="">// now returns 1 (wat?)</span></div></div><div class=""><div class=""><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(88, 126, 168); background-color: rgb(255, 255, 255);" class=""><span style="color: rgb(0, 0, 0);" class=""> view.</span>gestureRecognizers<span style="color: rgb(0, 0, 0);" class=""> = [foo, bar, baz]</span></div><div style="margin: 0px; font-stretch: normal; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(88, 126, 168); background-color: rgb(255, 255, 255);" class=""><span style="color: rgb(0, 0, 0);" class=""> view.</span>gestureRecognizers<span style="color: rgb(0, 0, 0);" class="">.</span>count<span style="color: rgb(0, 0, 0);" class=""> </span><span style="color: rgb(102, 139, 73);" class="">// still returns 1</span><span style="color: rgb(102, 139, 73);" class=""> </span><span style="color: rgb(102, 139, 73);" class="">(wat?!)</span></div></div></div><div class=""><span style="color: rgb(102, 139, 73);" class=""><br class=""></span></div><div class="">That is a recipe for torches and pitchforks right there. Yet it is analogous to what flatMap currently does.</div><div class=""><br class=""></div><div class="">Cheers,</div><div class=""><br class=""></div><div class="">Paul</div><div class=""><br class=""></div></div></body></html>