<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 2, 2017, at 6:18 PM, Tino Heth <<a href="mailto:2th@gmx.de" class="">2th@gmx.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Hi Gor,</div><div class=""><br class=""></div><div class="">[I'll continue to answer below, but that wont help you with your proposal…]</div><div class=""><br class=""></div><div class="">The question is wether this</div><div class=""><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><font color="#b92d5d" class="">protocol</font> <font color="#4f7a28" class="">Equatable</font> {</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><font color="#b92d5d" class="">static</font> <font color="#b92d5d" class="">func</font> == (_ some: <font color="#b92d5d" class="">Self</font>, _ other: <font color="#b92d5d" class="">Self</font>) -> <font color="#4f7a28" class="">Bool</font></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><font color="#b92d5d" class="">default</font> <font color="#b92d5d" class="">static</font> <font color="#b92d5d" class="">func</font> != (_ some: <font color="#b92d5d" class="">Self</font>, _ other: <font color="#b92d5d" class="">Self</font>) -> <font color="#4f7a28" class="">Bool</font></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class="">}</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><font color="#b92d5d" class="">extension</font> <font color="#4f7a28" class="">Equatable</font> {</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span></font><font color="#b92d5d" face="Menlo" class="">static</font><span class="" style="font-family: Menlo;"> </span><font color="#b92d5d" face="Menlo" class="">func</font><span class="" style="font-family: Menlo;"> != (_ some: </span><font color="#9a244f" class="" style="font-family: Menlo;">Self</font><span class="" style="font-family: Menlo;">, _ other: </span><font color="#9a244f" class="" style="font-family: Menlo;">Self</font><span class="" style="font-family: Menlo;">) -> </span><font color="#4f7a28" face="Menlo" class="">Bool</font><font face="Menlo" class=""> {</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><b class="">[<font color="#4d22b3" class="">Your Code Here]</font></b></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>}</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class="">}</font></div><div class=""><font face="Menlo" class=""><br class=""></font></div></div><div class="">is better than</div><div class=""><br class=""></div><div class=""><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><font color="#b92d5d" class="">protocol</font> <font color="#4f7a28" class="">Equatable</font> {</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><font color="#b92d5d" class="">static</font> <font color="#b92d5d" class="">func</font> == (_ some: <font color="#b92d5d" class="">Self</font>, _ other: <font color="#b92d5d" class="">Self</font>) -> <font color="#4f7a28" class="">Bool</font></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span></font><font color="#b92d5d" face="Menlo" class="">static</font><span class="" style="font-family: Menlo;"> </span><font color="#b92d5d" face="Menlo" class="">func</font><span class="" style="font-family: Menlo;"> != (_ some: </span><font color="#9a244f" class="" style="font-family: Menlo;">Self</font><span class="" style="font-family: Menlo;">, _ other: </span><font color="#9a244f" class="" style="font-family: Menlo;">Self</font><span class="" style="font-family: Menlo;">) -> </span><font color="#4f7a28" face="Menlo" class="">Bool</font><font face="Menlo" class=""> {</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span><b class="">[<font color="#4d22b3" class="">Your Code Here]</font></b></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>}</font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class=""><br class=""></font></div><div class="" style="background-color: rgb(255, 255, 255);"><font face="Menlo" class="">}</font></div><div class=""><font face="Menlo" class=""><br class=""></font></div><div class=""><font class="">I don't think so, and therefore, I don't want to add a new keyword (or, more precise, a new meaning for an existing keyword).</font></div></div><div class="">Both solutions could coexist, but I doubt that implementation inside protocol body leaves enough room for "default func".</div></div></div></blockquote><div><br class=""></div><div>I'll reiterate: the problem with the inline solution is that it forces all code to be bunched up in a single place and sacrifices readability.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">- Tino</div><div class=""><br class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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-size-adjust: auto; -webkit-text-stroke-width: 0px;"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class="">Fileprivate has been there for years, it just was called private — and because the "church of extensions" ;-) has been so powerful, we finally ended up with what we have now.</div></div></div></div></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Yes, I was here. The fact that we started off with private behaving the way it does now is history now. The point stands: extensions in the same file as the type definition have an extra guarantee that enable the compiler to provide extra features based on that: the guarantee that the extension and the type definition will always be visible simultaneously, thus, implicitly merging the extension into the type definition is possible. It's not possible to do in any other way, because a file is the only unit of compilation that's more-or-less guaranteed to be atomically parsed. A module is separated into files, which can be compiled into objects separately, making it impossible for the compiler to know if any extension in any of the other files will change the layout of the type.</div></div></div></div></blockquote><div class="">The compiler won't care where if a method is defined in the type declaration, or in an extension in the same file.</div><div class="">What extra guarantee could those extensions offer?</div></div></div></div></blockquote><div><br class=""></div><div>The extra guarantee that all non-same-file extensions don't have: the guarantee that the extension can be deterministically merged with the type definition before the type definition is emitted.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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-size-adjust: auto; -webkit-text-stroke-width: 0px;"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class=""><div class="">They are recommended in style guides, influencers blog about them, and they motivated a ridiculous complex change in the access rights system. Yet I haven't seen any evidence that they offer real benefit.</div></div></div></div></div></blockquote><div class=""><br class=""></div><div class=""><div class="">Extensions are a tool for decentralizing code. There are some critical limits on extensions that make main type definition subject to unavoidable bloating (required and designated initializers, stored properties, the deinitializer, and open methods), but everything else is a prime candidate for decentralizing. Putting as little code as possible into the type definition and semantically grouping the implementation into extensions improves readability and maintainability dramatically.</div></div></div></div></blockquote><div class="">The thing is: This is just a claim that gets repeated over and over. There is no proof, and I even don't know a single study on that topic.</div></div></div></div></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">Take a look at this article: </span><a href="https://en.wikipedia.org/wiki/Separation_of_concerns" class="">https://en.wikipedia.org/wiki/Separation_of_concerns</a></div></div></div></blockquote><div class="">There's nothing about Swift, neither about extensions, in this article.</div><div class="">I don't want to start throwing around buzzwords, but there's also <a href="https://en.wikipedia.org/wiki/Don't_repeat_yourself" class="">https://en.wikipedia.org/wiki/Don%27t_repeat_yourself</a></div></div></div></div></blockquote><div><br class=""></div><div>The Don't Repeat Yourself principle states that providing generic solutions to domains of problems is superior to providing largely similar solutions to specific problems. If anything, separating related bunches of code helps reduce extra work by localizing the code in a way that makes refactoring and debugging easier.</div><div>The separation of concerns is a well-known software design and implementation principle whereby code quality (which encompasses readability, maintainability, extensibility, portability) are improved through strict separation of logically unrelated (or loosely related) parts of the code. </div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><br class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class=""><div class="">Extensions are great for adding useful helpers to existing types, and still allow you to selectively expose details of your own classes — but most people seem to ignore those options and focus on something can be done better with plain old comments.</div></div></div></div></div></blockquote><div class=""><br class=""></div>Relying on comments for invariants and preconditions is a poor design decision, because there's no way of enforcing them and the whole integrity of the code is thrown at the mercy of a human's carefulness (which is a horrible fate to befall upon any code). By writing the code in such a way that makes it impossible to be misused (by way of compiler enforcement), the code becomes resilient and no amount of clumsy usage can lead to incredibly obscure bugs that would take a week of debugging to catch.</div></div></blockquote><div class="">But extensions are no tool to do so: They have no features that offer any protection, exactly like comments — they are just more typing and don't show up properly in Xcode.</div><div class=""><br class=""></div><div class=""><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">import</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>UIKit</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">class</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>MyViewController:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UIViewController</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(112, 61, 170);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">MyViewController</span><span class="" style="font-variant-ligatures: no-common-ligatures;">:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">UITableViewDataSource</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UITableView</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, numberOfRowslnSection:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">1</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UITableView</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, didSelectRowAt:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">IndexPath</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) {</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(62, 30, 129);">print</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures;">"Hu, isn't this a delegate method?"</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(112, 61, 170);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">extension</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">MyViewController</span><span class="" style="font-variant-ligatures: no-common-ligatures;">:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">UITableViewDelegate</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UITableView</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, numberOfRowsInSection:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">99</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>tableView:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UITableView</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, cellForRowAt indexPath:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">IndexPath</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UITableViewCell</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">let</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>cell =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">UITableViewCell</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(style: .</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(62, 30, 129);">default</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, reuseIdentifier:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(209, 47, 27);">""</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> cell.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">textLabel</span><span class="" style="font-variant-ligatures: no-common-ligatures;">?.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">text</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>=<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">"I should get my data from a datasource"</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>cell</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div></div><div class=""><br class=""></div><div class="">This is perfectly valid Swift, and it is build on extensions — but does it increase the quality of the code?</div><div class="">Same file extensions are nothing but a different pair of parenthesis to surround your code, and since Swift 4, you can shuffle around those delimiters however you like, and it has still the same meaning for the compiler.</div><div class="">They enforce nothing, and so far, I haven't seen any ideas to increase their power.</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">The compiler also doesn't stop you from making a wide variety of design choices, a comprehensive list of which can be found here: <a href="https://en.wikipedia.org/wiki/Anti-pattern#Programming" class="">https://en.wikipedia.org/wiki/Anti-pattern#Programming</a></div><div class="">For instance, have you tried reading the implementation of sin function in glibc? It's a very thick spaghetti code, sprinkled with a bucketful of magic numbers. It's absolutely impossible to comprehend.</div><div class=""><br class=""></div><div class="">Any language limitation should only be implemented if it passes the threshold where the gain of safety and convenience outweighs the loss of flexibility and the cost of implementing the limitation.</div><div class="">In your example, the gain of convenience is much lower than the cost of implementing it and loss of flexibility.</div></div></div></div></blockquote><div class="">What?</div><div class="">I didn't talk about adding limitations, and my example just shows that that "extension-oriented programming" doesn't add safety, just like comments — simply because the compiler strips both kinds of decoration.</div></div></div></div></blockquote><div><br class=""></div><div>Your example demonstrated a hypothetical lack of a compiler limitation that would make extensions more convenient and I demonstrated that such a limitation (namely, forcing protocol conformance and implementation of protocol requirements to be in a single extension) would not be a good idea.</div><div>Extensions are not decoration. They're at the very least access control tool. Extensions can have private members that are only visible to the extension and all other extensions in the same file. You can put many extensions into separate files and have them all operate on private members without exposing those private members and without having to bunch them all up into one place.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class=""><div class="">[sorry for the rant — but I think a critical look at extensions is long overdue: I rarely see someone questioning their role, so basically, we are making important decisions based on pure superstition]</div><div class=""><br class=""></div><div class="">A protocol itself is already a vehicle to group related methods,</div></div></div></div></div></blockquote><div class=""><br class=""></div>A protocol is a vehicle for generic programming and separation of abstractions.</div></div></blockquote><div class="">True — but does that stop a protocol from being a way to group related methods?</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Protocols are not free. They come at a cost of wrapping the object in an existential container and make indirect calls via the witness table. Extensions on value types are free.</div></div></div></div></blockquote></div>All true — but not an answer to the question ;-)</div></div></blockquote><br class=""></div><div>The answer is no. Extensions are specifically designed to group related methods and they have minimal overhead. Protocols have overhead (even if that overhead is not nearly as much as a class overhead) and serve the purpose of providing polymorphism. Protocols also pollute the global namespace and introduce complexity to the interface, so they also have an overhead of complexity. Extensions do none of those things.</div>Using protocols simply for bunching up related methods is similar to using a bulldozer for digging a hole in a sandbox.<div class=""><br class=""></div></body></html>