<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="">Structs behave _as if_ they are immutable and every mutation creates a copy.</div><div class=""><br class=""></div><div class="">The compiler may — and usually does — optimize this away as a direct mutation. (And then there’s inout, which is tricky.)</div><div class=""><br class=""></div><div class="">It’s a brilliant model, and I believe a strong one as it stands. Lino, I believe this addresses your #1 and #3. I’m afraid I don’t follow your #2. Can you elaborate?</div><div class=""><br class=""></div><div class="">Cheers, P</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 23, 2015, at 10:15 AM, Félix Cloutier 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="" style="font-family: HelveticaNeue; font-size: 13px; font-style: normal; font-variant: 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;">No, this is a consequence of structures being passed by value to property accessors. The getter doesn't return a reference to the frame, it returns a copy of it, so it is accompanied by a hidden set operation where it replaces the whole thing.</div><br class="" style="font-family: HelveticaNeue; font-size: 13px; font-style: normal; font-variant: 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;"><div class="" style="font-family: HelveticaNeue; font-size: 13px; font-style: normal; font-variant: 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 class="Apple-style-span" style="border-collapse: separate; font-family: 'Lucida Grande'; line-height: normal; border-spacing: 0px;">Félix</span></div><br class="" style="font-family: HelveticaNeue; font-size: 13px; font-style: normal; font-variant: 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;"><div style="font-family: HelveticaNeue; font-size: 13px; font-style: normal; font-variant: 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="">Le 23 déc. 2015 à 11:09:43, Kevin Lundberg via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><span class="" style="font-family: LucidaGrande; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;">I believe Ian is correct in that changing any struct's value in any way creates a whole new struct.</span><div class="" style="font-family: LucidaGrande; font-size: 12px; font-style: normal; font-variant: 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;">See <a href="http://swiftstub.com/635749345" class="">http://swiftstub.com/635749345</a><span class="Apple-converted-space"> </span>for proof (the didSet property observer fires every time a change happens to the struct).</div><div class="" style="font-family: LucidaGrande; font-size: 12px; font-style: normal; font-variant: 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;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Dec 23, 2015, at 11:00 AM, Lino Rosa 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 dir="ltr" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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;">Reassigning structures will create new ones. Mutating functions and reassigning its properties won't: they mutate it.<br class=""><div class="gmail_quote"><div dir="ltr" class="">On Wed, Dec 23, 2015 at 10:51 AM Ian Ynda-Hummel <<a href="mailto:ianynda@gmail.com" target="_blank" class="">ianynda@gmail.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;">I thought structures were immutable and mutating functions actually just created new structures, thus maintaining the by value semantics.<br class=""><div class="gmail_quote"></div><div class="gmail_quote"><div dir="ltr" class="">On Wed, Dec 23, 2015 at 10:45 AM Lino Rosa via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:<br class=""></div></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><div dir="ltr" class=""><div class="">I believe the language would be improved by making structures immutable.</div><div class=""><br class=""></div><div class="">1) The choice between classes and structures isn’t clear right now. If structures were immutable it would be natural to use them as value objects.</div><div class=""><br class=""></div><div class="">2) Refactoring a mutable structure into a class when it’s being passed around multiple threads removes the by-value semantics seamlessly. The resulting mutable class isn’t thread-safe.</div><div class=""><br class=""></div><div class="">2.1) Even when passed around a single thread, the resulting class would be passed by reference, so any mutations would have unintended consequences.</div><div class=""><br class=""></div><div class="">3) We could probably remove some syntax: `mutating` keyword and variable parameters. Also the `var` keyword before a structure could be used to denote reassignment (not mutability), just as it does with classes.</div><div class=""><br class=""></div><div class="">Of corse I might not be seeing the whole picture, so please weigh in.</div></div></blockquote></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-color: rgb(204, 204, 204); border-left-style: solid; padding-left: 1ex;"><img src="https://u2002410.ct.sendgrid.net/wf/open?upn=t5fkNsX-2F7-2FAygTFNPNE08PALgkjkO6I8wpsdssDS0uhzD3EyON0qfaM-2BbDYaPGa4azavBvUgXrcfIjbzgpxE8eP9166AITzK3ots1xL7ZbX7ZYqgZjOge2IKsot-2FFjNUORr0LjCExRUPumI8I-2BZoBO7yyqFqYpqCAk5TqOB5aWgB9OMHq0v4txo-2BHeGuoLN9wTozGfCQnGAys309-2B-2Biow4Vc-2FxAZMKOilKYVoGIgGMI-3D" alt="" width="1" height="1" border="0" class="" style="min-height: 1px !important; width: 1px !important; border-width: 0px !important; margin: 0px !important; padding: 0px !important;"><span class="Apple-converted-space"> </span>_______________________________________________<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" rel="noreferrer" target="_blank" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></blockquote></div></blockquote></div></div><img src="https://u2002410.ct.sendgrid.net/wf/open?upn=AxVqvhl7qaAz-2FE20TrrgNT-2F44XdgxmRgRA416dJII-2BS-2BJDOiVIu0C2Vav56WR9LMUCN4ixgGy1FMCLSy4WDlPnLDLlfm4ykymGh7BovnNSIawVpbDYNtfTTx-2FHQ3C0oHzqEN54vbWFeDkkzfRiUsNSozCP26069l-2BKWwkQum0w9hj0eCrRdMn9s19weZHzHDmwi2UC2-2Fcu-2B45iQFLAzGXht9DnjiNHMjDuNyOTw6Xw4-3D" alt="" width="1" height="1" border="0" class="" style="font-family: Helvetica; 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