<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=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Oct 17, 2017, at 12:54 PM, Benjamin G <<a href="mailto:benjamin.garrigues@gmail.com" class="">benjamin.garrigues@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Thanks for the post, that's the first clear explanation i see on this thread for the concepts behind the design for Sequence.<div class=""><br class=""></div><div class="">I am a bit afraid that understanding all that is a bit above what to expect the average swift developer will guess when he sees functions like "prefix / first / elementEqual (or whatever it's called)" on the Set type.</div><div class="">There is, IMHO, a much higher chance he'll either : </div><div class="">1/ not understand anything, or </div><div class="">2/ think Sets are in fact secretely ordered sets, or start writing generic extensions above Sequence or Collection thinking those protocols are synonymous for orderer collections.<br class=""><div class=""><br class=""></div><div class="">1/ is pretty harmless, but 2/ seems like a source of bug.</div><div class=""><br class=""></div><div class="">My personal opinion after reading all this is that we should simply change the name</div></div></div></div></blockquote><div><br class=""></div><div>Exactly, and that’s what Xiaodi’s proposal does. Confronted with these complexities, his proposal reasons that a name change is the lessor or evils, as in the “Proposed solution” section.</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><div class=""> to sequentiallyEquals</div></div></div></div></blockquote><div><br class=""></div><div><div>Xiaodi floated “lexicographicallyEqual” which is accurate and a big improvement, and I’m liking it more and more. I floated “sequentiallyEquals”, which I’m liking less and less now. My current preference is for “elementsOrderedEqual” which I think is more descriptive but unwieldy. On the other hand, this is a far less common facility, and order matters, so maybe more verbose names are fine.</div><div><br class=""></div><div>As you can tell, I’m pretty wishy-washy with names and probably should abstain from bike shedding anything important ;-)</div><div class=""><br class=""></div></div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><div class=""> (just because it let people hint at where this function comes from, and not let them believe that it's something native to the Set type), and not touch anything else, until maybe we someday have a way to make everything perfect for everyone.</div><div class=""><br class=""></div></div></div></div></blockquote><div><br class=""></div><div>We can ease the pain a bit. E.g. warnings/deprecation when the type is concretely known to be Set, etc. Not a general solution, but might fight some bugs.</div><div><br class=""></div><div>I think that of all the dichotomies we fail to model in our protocol hierarchy, the ordered vs unordered is the least useful to accommodate. It is, however, easy and fun to bike shed.</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><div class="gmail_extra"><div class="gmail_quote">On Tue, Oct 17, 2017 at 8:47 PM, Michael Ilseman via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word;line-break:after-white-space" class=""><div dir="auto" style="word-wrap:break-word;line-break:after-white-space" class=""><br class=""><div class=""><span class=""><br class=""><blockquote type="cite" class=""><div class="">On Oct 17, 2017, at 10:15 AM, Kevin Nattinger via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class="m_349660706971374135Apple-interchange-newline"><div class=""><div style="word-wrap:break-word" class=""><div class=""><blockquote type="cite" class=""><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" class=""><div class="gmail_quote"><div dir="auto" class="">Because, in my analysis, the problem is that the method is incorrectly named. The problem affects all types that conform to Sequence and not just Set and Dictionary; elementsEqual is a distinct function from ==, and it must either continue to be distinct or cease to exist, but its name does nothing to clarify any distinction.</div></div></div></blockquote><div class=""><br class=""></div>In my analysis, the problem is the method's implementation. As I see it, the only use for `elementsEqual` is as a replacement for `==` when two objects are different types (or not known to be the same)—equal elements, and IF the sequences have an order, in the same order. Could you provide an example where `elementsEqual` randomly returning either true or false depending on internal state alone is a legitimate and desirable result?</div><div class=""><br class=""></div></div></div></blockquote><div class=""><br class=""></div></span><div class="">It doesn’t randomly return true or false, it consistently returns true or false for the *same* pair of Sequences. What *same* means, of course, is complicated and exists at two levels (as we have two ways of talking about *same*). </div><div class=""><br class=""></div><div class="">I apologize for not reading every email in depth in this thread (they are coming in faster than I can parse them), but let me try to present motivation for this and hopefully provide more shared understanding.</div><div class=""><br class=""></div><div class=""><div class="">We have two forms of equality we’re talking about: equality of Sequence and equality of the elements of Sequences in their respective ordering. `==` covers the former, and I’ll use the existing (harmful) name of `elementsEqual` for the latter.</div><div class=""><br class=""></div><div class="">`==` conveys substitutability of the two Sequences. This does not necessarily entail anything about their elements, how those elements are ordered, etc., it just means two Sequences are substitutable. `elementsEqual` means that the two Sequences produce substitutable elements. These are different concepts and both are independently useful.</div><div class=""><br class=""></div><div class="">Cases:</div><div class=""><br class=""></div><div class="">1. Two Sequences are substitutable and produce substitutable elements when iterated. `==` and `elementsEqual` both return true. </div><div class=""><br class=""></div><div class="">Example: Two arrays with the same elements in the same order.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">2. Two Sequences are substitutable, but do not produce substitutable elements when iterated. `==` returns true, while `elementsEqual` returns false.</div><div class=""><br class=""></div><div class="">Example: Two Sets that contain the same elements but in a different order.</div><div class=""><br class=""></div><div class="">Contrived Example: Two Lorem Ipsum generators are the same generator (referentially equal, substitutable for the purposes of my library), but they sample the user’s current battery level (global state) each time they produce text to decide how fancy to make the faux Latin. They’re substitutable, but don’t generate the same sequence.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">3. Two Sequences are not substitutable, but produce substitutable elements when iterated. `==` returns false, while `elementsEqual` returns true.</div><div class=""><br class=""></div><div class="">Example: Consider two sequences that have differing identity. `==` operates on an identity level, `elementsEqual` operates at an element level.</div><div class=""><br class=""></div><div class="">Contrived Example: InfiniteMonkeys and Shakespeare both produce the same sonnet, but they’re not substitutable for my library’s purposes. </div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">4. Two Sequences are not substitutable and don’t produce substitutable elements when iterated. `==` and `elementsEqual` both return false.</div><div class=""><br class=""></div><div class="">Example: `[1,2,3]` compared to `[4,5,6]`</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">It is true that situations #2 and #3 are a little harder to grok, but they are what illustrate the subtle difference at hand. I think situation #2 is the most confusing, and has been the primary focus of this thread as Set exists and exhibits it.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Now, onto naming. `elementsEqual` is a very poor choice of name for the concept of equality of elements in their respective orderings, as it doesn’t highlight the “in their respective orderings” part. `lexicographicallyEqual` highlights the ordering much better, as “abc” is not lexicographically equal to “cba” despite having equal elements. I think it is clearly an improvement over the status quo. I like something a little more explicit (e.g. `elementsOrderedEqual`), personally, but I don’t care that strongly. I’m just glad to see `elementsEqual` getting some clarification.</div><div class=""><br class=""></div></div><span class=""><div class=""><br class=""></div><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap:break-word" class=""><div class=""><blockquote type="cite" class=""><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" class=""><div class="gmail_quote"><div dir="auto" class=""><br class=""></div><blockquote class="gmail_quote" style="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=""></div><div class="">Thanks,</div><div class="">Jon</div></div></blockquote></div></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;float:none;display:inline!important" class="">______________________________<wbr class="">_________________</span><br 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=""><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;float:none;display:inline!important" class="">swift-evolution mailing list</span><br 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=""><a href="mailto:swift-evolution@swift.org" 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" target="_blank" class="">swift-evolution@swift.org</a><br 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=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" 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" target="_blank" class="">https://lists.swift.org/<wbr class="">mailman/listinfo/swift-<wbr class="">evolution</a></blockquote></div><br class=""></div>______________________________<wbr class="">_________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" target="_blank" class="">https://lists.swift.org/<wbr class="">mailman/listinfo/swift-<wbr class="">evolution</a><br class=""></div></blockquote></span></div><br class=""></div></div><br class="">______________________________<wbr class="">_________________<br class="">
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