<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">Personally I think a great compromise is just forcing the user to use the `override` keyword when subclassing in these cases. That way the library maker can mark classes that aren't supported or are internal and ideally shouldn't be used by the programmer.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">However we shouldn't baby sit programmers, we are smart people after all. So if there is a huge catastrophic bug that just happens to be easily solvable by subclassing or whatever then we should allow them to do so.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">An `override` keyword would be a great compromise, take this class:</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><pre style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;font-stretch:normal;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;border-radius:3px;color:rgb(51,51,51);background-color:rgb(247,247,247)"><span class="" style="color:rgb(167,29,93)">public</span> <span class="" style="color:rgb(167,29,93)">class</span> NonSubclassableParentClass {</pre><pre style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;font-stretch:normal;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;border-radius:3px;color:rgb(51,51,51);background-color:rgb(247,247,247)">}</pre></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">If the programmer subclasses it normally, the compiler will throw an error telling them to use the `override` keyword to subclass non-subclassble classes:</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><pre style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;font-stretch:normal;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;border-radius:3px;color:rgb(51,51,51);background-color:rgb(247,247,247)"><span class="" style="color:rgb(167,29,93)">override</span> <span class="" style="color:rgb(167,29,93)">class </span> MySubclass: NonSubclassableParentClass {</pre><pre style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:13.6px;margin-top:0px;margin-bottom:0px;font-stretch:normal;line-height:1.45;word-wrap:normal;padding:16px;overflow:auto;border-radius:3px;color:rgb(51,51,51);background-color:rgb(247,247,247)">}</pre></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">Now there is a clear indicator that we are doing something not safe or ideal here. This is similar how the "!" in IUO indicates we have a unsafe value. We are grown-ups we should be able to know when to subclass but this doesn't mean there couldn't be something like this to indicate to the user that they may want to revaluate this in the future. </div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">So in the future other programmers can see this marker and think "Oh we are using this class in a non recommended way, so when it breaks when I upgrade the library it's our fault." hopefully making them continue to upgrade rather than not upgrading because it breaks "my subclass".</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">Whats great about this feature is it also allows linters or the compiler to also show warnings when this is used as well, that way those of us that are bugged by the amount of warnings we have in our app can endevour to fix it.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">In Ruby there is a convention to have these sort of monkey patches and subclasses to fix bugs in a special folder with "_ext" after it to indicate that this an extension to a class from a library, this indicates to the programmer that it's something we should ideally remove as soon as the app can work without that hack.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)">So I can't see why we can't have this `override` keyword to tell the library developer that we like to live life on the edge a litte ;)</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif;font-size:small;color:rgb(0,0,0)"><br></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr">
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<br><div class="gmail_quote">On 8 July 2016 at 22:14, Tino Heth via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></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"><span class=""><div><br><blockquote type="cite"><div><div dir="auto"><div><div><blockquote type="cite" style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div><div>When was the last time you you thought "I really wish the author of that library had restricted my options to use it"?</div></div></blockquote><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br></div><div style="font-family:Helvetica;font-size:12px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">I really wish Objective-C had this feature from the start. I believe there would have been significant benefits to Apple's platforms and ecosystem. The reasons for believing (or not believing) this have been discussed in depth so there isn't a need to rehash them now.</div></div></div></div></div></blockquote></div></span>I'm not asking for reasons but for a single persuasive example…<div><br></div><div>It is easy to claim that everything will be better if we add restrictions, but so far, I haven't heard of any real problems cause by the current defaults:</div><div>The motivation to change them is not because of actual experience, it's just the trendy opinion that inheritance is evil.</div></div><br>_______________________________________________<br>
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