<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="">Hi Jordan,<div class=""><br class=""></div><div class="">Thanks for the advice.</div><div class=""><br class=""></div><div class="">What if a subclass does implement hashValue differently? It seems you are saying a subclass should never override hashValue? Should Set not compare elements with == instead of hashValue?<br class=""><div class=""><br class="webkit-block-placeholder"></div><div class="">
Thanks<br class="Apple-interchange-newline"><span style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; display: inline !important; float: none;" class="">Nick</span><br style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; display: inline !important; float: none;" class="">M: +44 (0)7986 048 141</span><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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="">W: <a href="http://nickbrook.me" class="">http://nickbrook.me</a></div>
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<br class=""><div><blockquote type="cite" class=""><div class="">On 1 Sep 2016, at 23:55, Jordan Rose <<a href="mailto:jordan_rose@apple.com" class="">jordan_rose@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div 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-stroke-width: 0px;" class=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">On Sep 1, 2016, at 15:44, Zhao Xin via swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="gmail_default" style="font-family: georgia, serif;">Hi Nick,</div><div class="gmail_default" style="font-family: georgia, serif;"><br class=""></div><div class="gmail_default" style="font-family: georgia, serif;">Glad to help.</div><div class="gmail_default" style="font-family: georgia, serif;"><br class=""></div><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;">but when using third party classes I don’t know if the hash values are comparable<br class=""></blockquote><div class=""><br class=""></div><div class="gmail_default" style="font-family: georgia, serif;">You can create an extension with a convenient init(:), which creates a new instance of the super class basing on the instance of the sub class. That will guarantee the subtraction. Below code works in Xcode 7.3.1 with Swift 2.2.<br class=""></div><div class="gmail_default" style="font-family: georgia, serif;"><br class=""></div><div class="gmail_default"><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">import</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Foundation</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>==(lhs:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, rhs:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Foo</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);">Bool</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>lhs.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">id</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>== rhs.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">id</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(112, 61, 170);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">class</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Foo:</span><span class="" style="font-variant-ligatures: no-common-ligatures;">Hashable</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 162);">let</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>id:</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 162);">var</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>hashValue:<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="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 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(79, 129, 135);">id</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;" class=""><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><br class="webkit-block-placeholder"></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 162);">required</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(187, 44, 162);">init</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>id:</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></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">id</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>= id</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">class</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Bar:</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 162);">override</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(187, 44, 162);">var</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>hashValue:<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="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><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(187, 44, 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(79, 129, 135);">id</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; color: rgb(39, 42, 216);">5</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">var</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>fooSet:</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Set</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">> = [</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">10</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);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">9</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);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">8</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);">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">7</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)]</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">var</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>barSet:</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Set</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Bar</span><span class="" style="font-variant-ligatures: no-common-ligatures;">> = [</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Bar</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">8</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);">Bar</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">7</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);">Bar</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">6</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);">Bar</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(39, 42, 216);">5</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)]</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;">//fooSet.subtract(barSet) // error: cannot invoke 'subtract' with an argument list of type '(Set<Bar>)'</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(79, 129, 135);"><span class="" style="font-variant-ligatures: no-common-ligatures;">fooSet</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;">fooSet</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(61, 29, 129);">subtract</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures;">barSet</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(187, 44, 162);">as</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);">Set</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures;">Foo</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>) </span><span class="" style="color: rgb(0, 132, 0); font-family: menlo;">// works, but not what we want</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">fooSet</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(61, 29, 129);">forEach</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; color: rgb(61, 29, 129);">print</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</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><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(209, 47, 27);">(</span><span class="" style="font-variant-ligatures: no-common-ligatures;">$0.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">dynamicType</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(209, 47, 27);">), id:</span><span class="" style="font-variant-ligatures: no-common-ligatures;">\</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;">$0.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">id</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="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;">/*</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> Foo, id:7</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> Foo, id:10</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> Foo, id:9</span></div><div class="" style="font-family: menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;">*/</span></div></div></div></div></blockquote><br class=""></div><div 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-stroke-width: 0px;" class="">This isn't really a sensible thing to do. The rules for Hashable require that `a == b` implies `a.hashValue == b.hashValue`, and `a.hashValue != b.hashValue` implies `a != b`. If you break these rules you're going to have problems no matter what static types you're using.</div><div 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-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; 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="">Upcasting from Set<Bar> to Set<Foo> is the most concise way to solve this problem.</div><div 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-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; 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="">Jordan</div></div></blockquote></div><br class=""></div></body></html>