<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Hi Gwendal, these are use cases for using indices as unordered references which certainly are useful. I was looking for use cases depending on the order exposed by Sequence, specifically use cases for elementsEqual.</div><div><br></div><div>-Thorsten </div><div><br>Am 17.10.2017 um 09:03 schrieb Gwendal Roué <<a href="mailto:gwendal.roue@gmail.com">gwendal.roue@gmail.com</a>>:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8"><div><blockquote type="cite" class=""><div class=""><blockquote type="cite" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;" class=""><div class=""><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><div class="">Modeling is, by definition, imperfect. The question is, what imperfect model is most useful _to Swift_. The idea is that conforming Set and Dictionary to Collection is on balance more useful than not doing so; that having two protocols, Sequence and Collection, is on balance more useful than having one or three, and that the set of semantic guarantees of Collection are on balance more useful than other possible sets of semantic guarantees.<br class=""></div></div></div></div></div></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">That is your idea which is disputed and underlined with arguments whereas you keep repeating that Set behaves as dictated by its conformance without giving use cases why this should be useful.</span></div></blockquote><br class=""></div><div>Hello,</div><div><br class=""></div><div><div class="">You can't *control* the ordering of a set or a dictionary, but you can still *rely* on it.</div></div><div><br class=""></div><div class="">For example, to find a key in a dictionary that is associated a given value, you can rely on the fact that a dictionary's order is guaranteed to be stable, and that on top of that its indexes can address the dictionary itself, but also its keys and values sequences. The code below has no bug;</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27); background-color: rgb(255, 255, 255);" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="color: #ba2da2" class="">let</span><span style="color: #000000" class=""> dict = [</span>"a"<span style="color: #000000" class="">: </span>"foo"<span style="color: #000000" class="">, </span>"b"<span style="color: #000000" class="">: </span>"bar"<span style="color: #000000" class="">, </span>"c"<span style="color: #000000" class="">: </span>"needle"<span style="color: #000000" class="">]</span></div><div style="margin: 0px; font-size: 12px; line-height: normal; font-family: Helvetica; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(0, 132, 0);" class="">// Find a key associated with "needle"</div><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class=""><span style="color: #ba2da2" class="">if</span> <span style="color: #ba2da2" class="">let</span> index = dict.values.index(of: <span style="color: #d12f1b" class="">"needle"</span>) {</div><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class=""> <span style="color: #ba2da2" class="">let</span> key = dict.keys[index]</div><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class=""> print(key) <span style="color: #008400" class="">// prints "c"</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class="">}</div><div class=""><br class=""></div></div></div><div class="">It's more difficult to find a use case for set's ordering and indexes. But since you ask, here is an example. The goal is to find any element which is not equal to another value, in any collection:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="color: #ba2da2" class="">extension</span> <span style="color: #703daa" class="">Collection</span> <span style="color: #ba2da2" class="">where</span> Element: Equatable {</div><div style="margin: 0px; line-height: normal; color: rgb(0, 116, 105);" class=""><span style="color: #000000" class=""> </span>/// Returns any element which is not equal to the given element</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">func</span> anyElement(notEqualTo v: <span style="color: #703daa" class="">Element</span>) -> <span style="color: #703daa" class="">Element</span>? {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">if</span> <span style="color: #ba2da2" class="">let</span> i = <span style="color: #3e1e81" class="">index</span>(of: v) {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">if</span> <span style="color: #ba2da2" class="">let</span> alt = <span style="color: #3e1e81" class="">index</span>(i, offsetBy: <span style="color: #272ad8" class="">1</span>, limitedBy: <span style="color: #703daa" class="">endIndex</span>), alt != <span style="color: #703daa" class="">endIndex</span> {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">return</span> <span style="color: #ba2da2" class="">self</span>[alt]</div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">if</span> i == <span style="color: #703daa" class="">startIndex</span> {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">return</span> <span style="color: #ba2da2" class="">nil</span></div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">return</span> <span style="color: #703daa" class="">first</span></div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">return</span> <span style="color: #703daa" class="">first</span></div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class="">}</div><div style="margin: 0px; font-size: 12px; line-height: normal; font-family: Helvetica; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #703daa" class="">Set</span>([<span style="color: #272ad8" class="">1</span>, <span style="color: #272ad8" class="">2</span>, <span style="color: #272ad8" class="">3</span>]).<span style="color: #31595d" class="">anyElement</span>(notEqualTo: <span style="color: #272ad8" class="">1</span>) <span style="color: #008400" class="">// 2 or 3</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #703daa" class="">Set</span>([<span style="color: #272ad8" class="">1</span>, <span style="color: #272ad8" class="">2</span>]).<span style="color: #31595d" class="">anyElement</span>(notEqualTo: <span style="color: #272ad8" class="">1</span>) <span style="color: #008400" class="">// 2</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #703daa" class="">Set</span>([<span style="color: #272ad8" class="">1</span>]).<span style="color: #31595d" class="">anyElement</span>(notEqualTo: <span style="color: #272ad8" class="">1</span>) <span style="color: #008400" class="">// nil</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #703daa" class="">Set</span>([<span style="color: #272ad8" class="">2</span>]).<span style="color: #31595d" class="">anyElement</span>(notEqualTo: <span style="color: #272ad8" class="">1</span>) <span style="color: #008400" class="">// 2</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #703daa" class="">Set</span>([]).<span style="color: #31595d" class="">anyElement</span>(notEqualTo: <span style="color: #272ad8" class="">1</span>) <span style="color: #008400" class="">// nil</span></div><div style="margin: 0px; font-size: 12px; line-height: normal; font-family: Helvetica; min-height: 14px;" class=""><br class=""></div></div></div><div class="">That *can* be useful, isn't it?</div><div class=""><br class=""></div><div class="">Gwendal Roué</div><div class=""><br class=""></div></div></blockquote></body></html>