<div dir="ltr">&quot;required&quot; also doesn&#39;t mean that a subclass has to implement the required initializer since it can be inherited.<div>Your example is an abstract function which should have it&#39;s own keyword (if we ever get abstract functions).<br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Dec 16, 2015 at 7:37 PM, Vester Gottfried <span dir="ltr">&lt;<a href="mailto:vester.gottfried@gmail.com" target="_blank">vester.gottfried@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">I think reusing required would send the wrong message. Required would mean for me something like NSOperation subclasses maybe require to have a main() function, but that doesn&#39;t mean you have to call super. On the contrary, the documentation of NSOperation main() explicitly states not to call super. </div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Dec 16, 2015 at 7:08 PM, Marc Knaup <span dir="ltr">&lt;<a href="mailto:marc@knaup.koeln" target="_blank">marc@knaup.koeln</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">What about re-using the &quot;required&quot; keyword in the superclass which already means something similar for initializers?<div>Subclass implementations are required to call super&#39;s implementation.<br><div>If a subclass doesn&#39;t implemented the required method it could mean that it inherits the behavior from the superclass - just like initializers can be inherited too.</div></div></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Dec 16, 2015 at 7:02 PM, Jordan Rose <span dir="ltr">&lt;<a href="mailto:jordan_rose@apple.com" target="_blank">jordan_rose@apple.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>+1 from me. FWIW, the Objective-C one is syntactic.</div><div><br></div><div>Information from Radar: the request for this is <a>rdar://problem/17408107</a> (plus a few duplicates). One of the dups suggests a variation where a subclass method can be declared as &quot;refine&quot; instead of &quot;override&quot; so that you can document that your <i>own</i> method is expected to call super. In this model, &quot;@requires_super&quot; could become something like &quot;imposed&quot;. I personally think this doesn&#39;t add enough, especially since we wouldn&#39;t be publishing refine-vs-override in a library&#39;s public interface.</div><span><font color="#888888"><div><br></div><div>Jordan</div></font></span><div><div><br><div><blockquote type="cite"><div>On Dec 16, 2015, at 9:49 , Marc Knaup via swift-evolution &lt;<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>&gt; wrote:</div><br><div><div dir="ltr" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">Sounds reasonable since even the best flow analysis cannot ensure that all codepaths call the super implementation.<div><br></div><div>Some more edge cases:</div><div><ul><li>Calling super asynchronously by using it in a closure</li><li>Referring to the super implementation by assign it to a variable and call it later (is that really possible? never did that)</li></ul></div></div><div class="gmail_extra" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br><div class="gmail_quote">On Wed, Dec 16, 2015 at 6:25 PM, Vester Gottfried<span> </span><span dir="ltr">&lt;<a href="mailto:vester.gottfried@gmail.com" target="_blank">vester.gottfried@gmail.com</a>&gt;</span><span> </span>wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">I would suggest that @requires_super only checks if a call to super is present at all. More detailed behaviour should be part of the functions documentation, because I think all possibilities cannot be checked easily by the compiler. For example a call to super my be required to happen early or late inside the function. But when too early or too late is can probably not been forseen by the compiler.</div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Dec 16, 2015 at 5:46 PM, Marc Knaup<span> </span><span dir="ltr">&lt;<a href="mailto:marc@knaup.koeln" target="_blank">marc@knaup.koeln</a>&gt;</span><span> </span>wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">+1 always had such issues with UIViewController&#39;s lifecycle methods.<div><br></div><div>But edge cases need to be considered like &quot;throws&quot; for example.</div><div>Do I need to call super before I throw something?</div></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Dec 16, 2015 at 5:41 PM, Matthew Johnson via swift-evolution<span> </span><span dir="ltr">&lt;<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>&gt;</span><span> </span>wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word">+1 to this.  Anything that helps ensure inheritance is thought through carefully and used correctly is a win.<div><br><div><blockquote type="cite"><div><div><div>On Dec 16, 2015, at 10:32 AM, Vester Gottfried via swift-evolution &lt;<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>&gt; wrote:</div><br></div></div><div><div><div><div dir="ltr"><div>Some class based libraries/frameworks expect the consumer to subclass certain classes and override specific method and require that the super implementation of an overridden method is being called.</div><div><br></div><div>Not calling the super implementation is a common source of bugs that may be prevented if the compiler checks if super is called, like it does in some cases of init().</div><div><br></div><div>Example:<br></div><div><br></div><div>class Box {</div><div>   @requires_super<br></div><div>   <span> </span>func addStuff() { ... }</div><div>}<br></div><div><br></div><div>Overriding class Box&#39;s addStuff without calling super.addStuff() should result in an error</div><div><br></div><div>class Chest : Box {</div><div>   <span> </span>override addStuff() {<br></div><div>         // ERROR: addStuff() requires call to super.addStuff()</div><div>       <span> </span>...</div><div>   <span> </span>}</div><div>}<br></div><div><br></div><div>Objective-C developers know this as NS_REQUIRES_SUPER and I think its worth thinking about adapting it.</div><div><div><br></div><div>I hope my proposal was clear and thanks for reading,</div><div><br></div></div><div>Gottfried</div></div></div></div><img src="https://u2002410.ct.sendgrid.net/wf/open?upn=eLFMrKDT8iBxZ-2Fbnk-2BZqvSchNN-2FvYXdceA0T7VxwkAfetdXVtelgzCfab-2Fp92fvLNUbxvC5Ukh9mTRYtT7oZ-2BzUDHQ-2FkLVfwWHuXGWvz7iaXCPo1KAcjPGxoZUQTW8DMleErzJnIt-2FRMb1-2FEM1WN-2BscY0xmKk-2BmXO16SS-2BCT9-2B7dgbk1nlmgpvH5cNha2dTvKe3-2FSntENn88F21K4ayGJlZuPediCmd1qI2SGJLz5ZQ-3D" alt="" width="1" height="1" border="0" style="min-height:1px!important;width:1px!important;border-width:0px!important;margin:0px!important;padding:0px!important"><span> </span>_______________________________________________<br>swift-evolution mailing list<br><a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a><br><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br></div></blockquote></div><br></div><img src="https://u2002410.ct.sendgrid.net/wf/open?upn=6ZGE61OxINd5lLe2xYh9Ku-2BXbixWNr2nvfzp2IB1sZh6TKQF8BMklGkmbYn3aAkB6MJpxZ0t4CiiE4yQ7c3-2F-2FxDq-2BE2nhnHvAuBkVBkwM6uDXj3Tn9ItDh6xxQ-2FkLlwiu1hYr6F53gyOSlV8vvG2QFLbE8T144o6I89KhIacPLr89IyBgLNJrrpOeDUJRbKLXLQQTW2cBkYK87e4-2B4ZzjRVbIK6-2FolcNdTCYIDUgxlA-3D" alt="" width="1" height="1" border="0" style="min-height:1px!important;width:1px!important;border-width:0px!important;margin:0px!important;padding:0px!important"></div><br>_______________________________________________<br>swift-evolution mailing list<br><a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a><br><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br><br></blockquote></div><br></div></div></div></blockquote></div><br></div></div></div></blockquote></div><br></div><img src="https://u2002410.ct.sendgrid.net/wf/open?upn=ZEz4qHYnXhPr3bBPu-2FxP4tN3HfWKL-2FtJpqkQ0gkOVSAZmDoVZgkFkAVq9xL32Cvop-2BxtPd01Ewb-2FmOGWtV3hST1BxIiVQiZ-2FcrCTXjW4avvFCWZI7WnIOtzUdNaGu0XflA8Kti-2BK6hq-2Bu6WTBpg-2B9WN9QvbEkBe54EbsctlV-2F2V6Yt8r5Ng1S1HbObIJRP-2BUmB10J2k720LdXFsurTutQ76sLkMDxTfICFGRpWnhEyg-3D" alt="" width="1" height="1" border="0" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;min-height:1px!important;width:1px!important;border-width:0px!important;margin:0px!important;padding:0px!important"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weig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