<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><div style="direction: inherit;"><br></div>Sent from my iPhone</div><div><br>On 23 Jul 2016, at 06:00, Wang LiMing via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div>
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<div class="">There’s two case :</div>
<div class=""> 1. Bug from customer’s code</div>
<div class=""> 2. Bug from library/Framwork’s code</div>
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<div class="">If we fix the case 1(forbidden subclass/overriding), means the library/framework’s author must fix case 2</div>
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<div class="">If want customer fix the case 2(allow subclass/overriding), means we can’t fix the case 1</div>
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<div class="">What’s our target? case 1 or case 2? </div></div></div></blockquote><div style="direction: inherit;"><br></div><div style="direction: inherit;">Beside input validation, proper use of failable initialisers, and exceptions... how and why would you target case 1 further as a library author practically? It sounds like something useful in some cases and noble in intention but also a bit of a slippery slope to patronising your users... you may as well write the whole code for then ;). Seriously though, what would your reasons be for case 1?</div><div style="direction: inherit;"><br></div><blockquote type="cite"><div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">
<div class="">Case 1 depends on the decision of case 2(customer fix or author fix)</div>
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<div class="">It’s big problem that can’t solved by language features.</div>
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<div class="">I think our target should be a language with better features that can improve the quality of code/product.</div>
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<div class="">在 2016年7月23日，上午2:39，Dave Abrahams via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> 写道：</div>
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Fri Jul 22 2016, Paul Cantrell <</span><a href="mailto:swift-evolution@swift.org" style="font-family: Helvetica; font-size: 14px; 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;" class="">swift-evolution@swift.org</a><span style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px; float: none; display: inline !important;" class="">>
wrote:</span><br style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px;" class="">
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<blockquote type="cite" class="">On Jul 22, 2016, at 3:15 AM, Dave Abrahams via swift-evolution<br class="">
<<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class="">
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I wrote that subclassability is not an important element of safety<br class="">
**independent of overriding**. If you don't allow any overriding,<br class="">
your code is always “resilient” enough to handle subclassing.<br class="">
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Code can make assumptions about a type having a fixed set of<br class="">
subclasses known at compile time:<br class="">
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switch foo {<br class="">
case is YinFoo:<br class="">
...<br class="">
case is YangFoo:<br class="">
...<br class="">
default:<br class="">
fatalError("only two kinds of Foo known")<br class="">
}<br class="">
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Granted, code like this is usually a sign of a flawed<br class="">
design. Reasonable uses for the “fixed, known set of subtypes” pattern<br class="">
are rare.<br class="">
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Design quality questions aside, however, it is not strictly true that<br class="">
preventing all member overrides guarantees that code is resilient to<br class="">
unexpected subclassing.<br class="">
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<span style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px; float: none; display: inline !important;" class="">Point
taken.</span><br style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px;" class="">
<br style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px;" class="">
<span style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px; float: none; display: inline !important;" class="">--<span class="Apple-converted-space"> </span></span><br style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px;" class="">
<span style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px; float: none; display: inline !important;" class="">Dave</span><br style="font-family: Helvetica; font-size: 14px; 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-stroke-width: 0px;" class="">
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