<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><p style="-webkit-print-color-adjust: exact; margin-right: 0px; margin-bottom: 15px; margin-left: 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2; margin-top: 0px !important;" class="">Hello Swift community:</p><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class="">Thank you for your reviews for my proposal. As you may have seen, this proposal contains two solutions originally:</p><ul style="-webkit-print-color-adjust: exact; margin: 15px 0px; padding-left: 30px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class=""><li style="-webkit-print-color-adjust: exact; margin: 0px;" class="">Compiler magic</li><li style="-webkit-print-color-adjust: exact; margin: 0px;" class="">Compile-time checking</li></ul><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class="">However even though <em style="-webkit-print-color-adjust: exact;" class="">Solution: Compiler magic</em> is viable, according to some of feedback from several reviewers, a developer who is new to Swift would continue to be misled by the introduction of the automatic copy behavior:</p><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class=""><em style="-webkit-print-color-adjust: exact;" class="">from Xiaodi Wu <a href="mailto:xiaodi.wu@gmail.com" style="-webkit-print-color-adjust: exact; color: rgb(65, 131, 196);" class="">xiaodi.wu@gmail.com</a>:</em></p><blockquote style="-webkit-print-color-adjust: exact; margin: 15px 0px; border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); padding: 0px 15px; color: rgb(119, 119, 119); font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class=""><div style="-webkit-print-color-adjust: exact; margin: 0px;" class="">A person who is new to Swift would continue to be confused if <code style="-webkit-print-color-adjust: exact; margin: 0px 2px; padding: 0px 5px; white-space: nowrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px;" class="">@NSCopying</code> had magic but <code style="-webkit-print-color-adjust: exact; margin: 0px 2px; padding: 0px 5px; white-space: nowrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px;" class="">didSet</code> and other behaviors did not. A person who has studied Swift and internalized the reasoning behind this initially tricky situation might rightly expect that <em style="-webkit-print-color-adjust: exact;" class="">all</em> behaviors, including <code style="-webkit-print-color-adjust: exact; margin: 0px 2px; padding: 0px 5px; white-space: nowrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px;" class="">@NSCopying</code>, are ignored during <code style="-webkit-print-color-adjust: exact; margin: 0px 2px; padding: 0px 5px; white-space: nowrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px;" class="">init</code>.</div></blockquote><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class=""><em style="-webkit-print-color-adjust: exact;" class="">from David Hart <a href="mailto:david@hartbit.com" style="-webkit-print-color-adjust: exact; color: rgb(65, 131, 196);" class="">david@hartbit.com</a>:</em></p><blockquote style="-webkit-print-color-adjust: exact; margin: 15px 0px; border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); padding: 0px 15px; color: rgb(119, 119, 119); font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class=""><div style="-webkit-print-color-adjust: exact; margin: 0px;" class="">For the same reasons as Xiaodi, this proposal could be potentially misleading if it introduces custom compiler magic, warning or errors that was not replicated for future property behaviours.</div></blockquote><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class="">For this consideration, I decided to lower the priority of <em style="-webkit-print-color-adjust: exact;" class="">Solution: Compiler magic</em> to <code style="-webkit-print-color-adjust: exact; margin: 0px 2px; padding: 0px 5px; white-space: nowrap; border: 1px solid rgb(234, 234, 234); background-color: rgb(248, 248, 248); border-radius: 3px;" class="">Alternatives Considered</code> section and leave <em style="-webkit-print-color-adjust: exact;" class="">Solution: Compile-time checking</em> as the only one major solution, which suggests that compiler warns the developers to call copy manually, rather than implicit magic:</p><blockquote style="-webkit-print-color-adjust: exact; margin: 15px 0px; border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); padding: 0px 15px; color: rgb(119, 119, 119); font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class=""><div style="-webkit-print-color-adjust: exact; margin: 0px;" class="">Have compiler emit a compile-time error or warning if developers are performing an assignment operation from within an initializer between a property declared as @NSCopying and an instance of a <nscopying style="-webkit-print-color-adjust: exact;" class="">protocol conforming class.</nscopying></div></blockquote><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class="">I’ve already submitted a pull-request for this modification.</p><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class="">Best,</p><p style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; font-variant-ligatures: normal; orphans: 2; widows: 2;" class="">Torin</p></body></html>