<html><head><meta http-equiv="Content-Type" content="text/html charset=gb2312"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">Hi All,</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">IĄ¯m coding for section like data structure. </div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">For example:</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">I have an Album struct, which has many MediaItems.</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">It has a sectioned property called "sectionedMediaItemInfos", which is an array of sections.</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">Each section represents for a disc, and </span>has an "items" array contains all MedaItems in that disc.</div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div class="">The define code is like:</div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">```Swift</span></div></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><div style="margin: 0px; line-height: normal; color: rgb(52, 149, 175);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">struct</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> Album</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> sectionedMediaItemInfos: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Sectioned</span><span style="font-variant-ligatures: no-common-ligatures" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">MediaItemInfo</span><span style="font-variant-ligatures: no-common-ligatures" class="">>]?</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div class=""><br class=""></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">struct</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Sectioned<Item> : </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">SectionProtocol</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> title: </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">String</span><span style="font-variant-ligatures: no-common-ligatures" class="">?</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> items: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Item</span><span style="font-variant-ligatures: no-common-ligatures" class="">]</span></div><p style="margin: 0px; line-height: normal; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">init</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures" class="">) {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">items</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = </span><span style="font-variant-ligatures: no-common-ligatures" class="">[]</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">title</span><span style="font-variant-ligatures: no-common-ligatures" class=""> = nil</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div></span></div></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">protocol</span><span style="font-variant-ligatures: no-common-ligatures" class=""> SectionProtocol {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">associatedtype</span><span style="font-variant-ligatures: no-common-ligatures" class=""> SectionItemType</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> items: [SectionItemType] { </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">get</span><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">```</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Now I want to define some extra properties for sections array</span>, like</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">"sectionMediaItemInfos"."itemsCount" that count all items in each sections.</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">So I can write that extension:</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code'; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""></span><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code'; min-height: 13px;" class="">```Swift</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">public</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">extension</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Array</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">where</span><span style="font-variant-ligatures: no-common-ligatures" class=""> Element : SectionProtocol {</span></div><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code'; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> itemsCount: </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">reduce</span><span style="font-variant-ligatures: no-common-ligatures" class="">(0) { (result, section) </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">in</span><span style="font-variant-ligatures: no-common-ligatures" class=""> result + section.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">items</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">count</span><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">}</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">```</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">So I can get my itemsCount with code like:</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">```Swift</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">album.sectionedMediaItemInfos.itemsCount</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">```</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">That looks good.</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">Then I want to define code to return all items in this sectioned property.</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">```Swift</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">extension</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">Array</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">where</span> Element : SectionProtocol {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; line-height: normal; color: rgb(52, 149, 175);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">var</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class=""> items: [</span><span style="font-variant-ligatures: no-common-ligatures;" class="">SectionProtocol</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class="">.</span><span style="font-variant-ligatures: no-common-ligatures;" class="">SectionItemType</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class="">] {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">return</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> .flatMap { $0.items }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">}</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">```</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class="">This doesnĄ¯t work. It reported as "Cannot use associated type 'SectionItemType' outside of its protocol"</div></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">The only way to achieve my goals is to untyped the extended "items" property:</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">```Swift</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">extension</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">Array</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">where</span> Element : SectionProtocol {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><div style="margin: 0px; line-height: normal; color: rgb(52, 149, 175);" class=""><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">var</span><span style="font-variant-ligatures: no-common-ligatures" class=""> items: [</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">Any</span><span style="font-variant-ligatures: no-common-ligatures" class="">] {</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">return</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.flatMap { $0.items }</span></div><div style="margin: 0px; line-height: normal; color: rgb(0, 0, 0);" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">}</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">```</span></div></span></div></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class="">Which is not perfect for this case.</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">So in this special case, I think allow use associated type outside of its protocol is necessary.</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">And we may allow define protocol with generic type. That would be more convenient.</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">```Swift</span></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal; color: rgb(52, 149, 175);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">struct</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class=""> Album</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 0, 0);" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> sectionedMediaItemInfos: [</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">Sectioned</span><span style="font-variant-ligatures: no-common-ligatures;" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">MediaItemInfo</span><span style="font-variant-ligatures: no-common-ligatures;" class="">>]?</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">}</span></div><div class=""><br class=""></div><div class=""><div style="margin: 0px; line-height: normal;" class=""><br class=""></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">struct</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> Sectioned<Item> : </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">SectionProtocol</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> title: </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">String</span><span style="font-variant-ligatures: no-common-ligatures;" class="">?</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> items: [</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">Item</span><span style="font-variant-ligatures: no-common-ligatures;" class="">]</span></div><div style="margin: 0px; line-height: normal; min-height: 13px;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><br class="webkit-block-placeholder"></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">init</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures;" class="">) {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">items</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> = </span><span style="font-variant-ligatures: no-common-ligatures;" class="">[]</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">title</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> = nil</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">}</span></div></span></div></div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><div class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">protocol</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> SectionProtocol<SectionItemType> {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">var</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> items: [SectionItemType] { </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">get</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> }</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">}</span></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">public</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">extension</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">Array</span> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">where</span> Element : SectionProtocol {</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="color: rgb(0, 0, 0); font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="color: rgb(4, 51, 255); font-variant-ligatures: no-common-ligatures;" class="">var</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> items: [<font color="#0433ff" class="">Element.</font></span>SectionItemType] {</div><div style="color: rgb(0, 0, 0); margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">return</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">self</span><span style="font-variant-ligatures: no-common-ligatures;" class="">.flatMap { $0.items }</span></div><div style="color: rgb(0, 0, 0); margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> }</span></div></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">}</span></div></span></div></div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">```</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">Thank all!</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">Jiannan</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: 'Fira Code';" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div></body></html>