<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Oct 16, 2017, at 1:05 PM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" class="">xiaodi.wu@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><br class=""><div class="gmail_quote"><div dir="auto" class="">On Mon, Oct 16, 2017 at 10:49 Jonathan Hull <<a href="mailto:jhull@gbis.com" class="">jhull@gbis.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Oct 16, 2017, at 7:20 AM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" target="_blank" class="">xiaodi.wu@gmail.com</a>> wrote:</div><br class="m_-3004557228007923799Apple-interchange-newline"><div class=""><blockquote class="gmail_quote" 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;margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word" class=""><div class="">To start with, the one you gave as an example at the beginning of this discussion: Two sets with identical elements which have different internal storage and thus give different orderings as sequences. You yourself have argued that the confusion around this is enough of a problem that we need to make a source-breaking change (renaming it) to warn people that the results of the ‘elementsEqual’ algorithm are undefined for sets and dictionaries.</div></div></blockquote><div dir="auto" 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" class=""><br class=""></div><div dir="auto" 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" class="">No, I am arguing that the confusion about ‘elementsEqual’ is foremost a problem with its name; the result of this operation is not at all undefined for two sets but actually clearly defined: it returns true if two sets have the same elements in the same iteration order, which is a publicly observable behavior of sets (likewise dictionaries).</div></div></blockquote></div><br class=""></div><div style="word-wrap:break-word" class=""><div class="">But that iteration order is undefined and could easily change due to changes in the private/internal structure of sets/dictionaries. Algorithms that rely on that “publicly observable behavior” (i.e. leaking of internals) will suddenly break.</div></div></blockquote><div dir="auto" class=""><br class=""></div><div dir="auto" class="">And an algorithm in which such “sudden breakage” would occur is…?</div></div></div></div></blockquote><div><br class=""></div><div>Here are a few off the top of my head:</div><div><br class=""></div><div>func hasPrefix(Sequence)->Bool</div><div>func hasSuffix(Sequence)->Bool</div><div>func containsSubsequence(Sequence)->Bool</div><div><br class=""></div><div>What do these methods mean with regards to Set’s “publicly observable behavior”?</div><br class=""><blockquote type="cite" class=""><div class=""><div class=""><div class="gmail_quote"><div dir="auto" class=""><br class=""></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><div class="">You keep claiming that this bug is a feature because it is the current behavior… but that is tautological reasoning.</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Jon</div></div></blockquote></div></div>
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