<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div><blockquote type="cite" class=""><div class="">On Mar 30, 2017, at 1:20 PM, Joshua Alvarado 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=""><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="">I think think the gain of functionality isn't there for the addition of this functionality to be added. There are other ways to implement what you are desiring to do without adding it to Swift language.</span></div></blockquote><br class=""></div><div>For instance, wrap your type in something like this:</div><div><br class=""></div><div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">struct</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> Recorded<Base: </span><span style="font-variant-ligatures: no-common-ligatures" class="">RangeReplaceableCollection</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> base: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">) {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">base</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = base</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">changes</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = [ </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures" class="">(newElements: base) ]</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">fileprivate(set)</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">var</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> base: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">fileprivate(set)</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">var</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> changes: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">]</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(186, 45, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">extension</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">final</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">class</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> Change: </span><span style="font-variant-ligatures: no-common-ligatures" class="">Hashable</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">, </span><span style="font-variant-ligatures: no-common-ligatures" class="">CustomStringConvertible</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> subrange: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Range</span><span style="font-variant-ligatures: no-common-ligatures" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index>?</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> newElements: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Iterator.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Element</span><span style="font-variant-ligatures: no-common-ligatures" class="">]</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class=""><C: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Collection</span><span style="font-variant-ligatures: no-common-ligatures" class="">>(subrange: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Range</span><span style="font-variant-ligatures: no-common-ligatures" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Index</span><span style="font-variant-ligatures: no-common-ligatures" class="">>? = </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">nil</span><span style="font-variant-ligatures: no-common-ligatures" class="">, newElements: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">C</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">where</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">C</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Iterator.Element == </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Iterator</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Element</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">subrange</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = subrange</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">newElements</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Array</span><span style="font-variant-ligatures: no-common-ligatures" class="">(newElements)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">static</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> == (lhs: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures" class="">, rhs: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures" class="">) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Bool</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> lhs === rhs</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> hashValue: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">ObjectIdentifier</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">).</span><span style="font-variant-ligatures: no-common-ligatures" class="">hashValue</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> description: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">String</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">if</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> subrange = </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">subrange</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"base[</span><span style="font-variant-ligatures: no-common-ligatures" class="">\</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">subrange.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">description</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">)] = </span><span style="font-variant-ligatures: no-common-ligatures" class="">\</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">newElements</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">description</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">)"</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">else</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">"base = </span><span style="font-variant-ligatures: no-common-ligatures" class="">\</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">newElements</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">description</span><span style="font-variant-ligatures: no-common-ligatures; color: #d12f1b" class="">)"</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> apply(to c: </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">inout</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures" class="">) {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> subrange = </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">subrange</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ?? c.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">startIndex</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ..< c.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">endIndex</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> c.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">replaceSubrange</span><span style="font-variant-ligatures: no-common-ligatures" class="">(subrange, with: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">newElements</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> c.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">changes</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">append</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">mutating</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> apply(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> changes: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures" class="">]) {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">for</span><span style="font-variant-ligatures: no-common-ligatures" class=""> change </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">in</span><span style="font-variant-ligatures: no-common-ligatures" class=""> changes {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> change.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">apply</span><span style="font-variant-ligatures: no-common-ligatures" class="">(to: &</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> newChanges(since older: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures" class="">) -> [</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures" class="">] {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> changes = </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">changes</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">guard</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> lastChange = older.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">changes</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">last</span><span style="font-variant-ligatures: no-common-ligatures" class="">,</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> i = changes.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">index</span><span style="font-variant-ligatures: no-common-ligatures" class="">(of: lastChange) </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">else</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> changes</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> overlapRange = </span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">0</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ... i</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(62, 30, 129);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">precondition</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> older.</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">changes</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">suffix</span><span style="font-variant-ligatures: no-common-ligatures" class="">(overlapRange.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">count</span><span style="font-variant-ligatures: no-common-ligatures" class="">) == changes[overlapRange],</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(209, 47, 27);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures" class="">"self includes old changes not present in older"</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> )</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> changes.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">removeSubrange</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #272ad8" class="">0</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ... i)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> changes</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; color: rgb(112, 61, 170);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">extension</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Recorded</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">: </span><span style="font-variant-ligatures: no-common-ligatures" class="">RangeReplaceableCollection</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">subscript</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> i: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Iterator.Element {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">get</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">base</span><span style="font-variant-ligatures: no-common-ligatures" class="">[i]</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">set</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">replaceSubrange</span><span style="font-variant-ligatures: no-common-ligatures" class="">(i ..< </span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">index</span><span style="font-variant-ligatures: no-common-ligatures" class="">(after: i), with: [newValue])</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> index(after i: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index) -> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3e1e81" class="">index</span><span style="font-variant-ligatures: no-common-ligatures" class="">(after: i)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> startIndex: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">startIndex</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> endIndex: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">endIndex</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">() {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">())</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><p style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input; min-height: 19px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">mutating</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">func</span><span style="font-variant-ligatures: no-common-ligatures" class=""> replaceSubrange<C>(</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class=""> subrange: </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Range</span><span style="font-variant-ligatures: no-common-ligatures" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Index>, with newElements: </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">C</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">where</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">C</span><span style="font-variant-ligatures: no-common-ligatures" class=""> : </span><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Collection</span><span style="font-variant-ligatures: no-common-ligatures" class="">,</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">C</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Iterator.Element == </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Base</span><span style="font-variant-ligatures: no-common-ligatures" class="">.Iterator.Element</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> change = </span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">Change</span><span style="font-variant-ligatures: no-common-ligatures" class="">(subrange: subrange, newElements: newElements)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> change.</span><span style="font-variant-ligatures: no-common-ligatures; color: #31595d" class="">apply</span><span style="font-variant-ligatures: no-common-ligatures" class="">(to: &</span><span style="font-variant-ligatures: no-common-ligatures; color: #ba2da2" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 13px; line-height: normal; font-family: Input;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class=""><br class=""></span></div></div><div class="">(This is begging for Swift 4's conditional conformance feature, which would allow `Recorded` to conform to `RandomAccessCollection` et.al. if the underlying type did.)</div><div class=""><br class=""></div><div class="">Now you have a ready-made change list, and all you need to do is write a `didSet` that runs `newChanges(since: oldValue)` on the new value and figures out what to do with it. That ought to be faster than a full difference calculation from scratch on every `didSet`.</div><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; border-spacing: 0px;"><div class=""><div style="font-size: 12px; " class="">-- </div><div style="font-size: 12px; " class="">Brent Royal-Gordon</div><div style="font-size: 12px; " class="">Architechies</div></div></span>
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