<div dir="ltr"><div class="gmail_default" style="font-family:georgia,serif">I don't see the point. For example if an element in Set<B> and another element in Set<A> are with a same hash value. Neither of the elements should be subtracted. As they are in different types. And hash values between different types are not guaranteed to be comparable. </div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif"><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">import</span><span style="font-variant-ligatures:no-common-ligatures"> Foundation</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(112,61,170)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">class</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> Foo:</span><span style="font-variant-ligatures:no-common-ligatures">Hashable</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> value: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"> </span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">public</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> hashValue: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">return</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"> </span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">public</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">static</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">func</span><span style="font-variant-ligatures:no-common-ligatures"> ==(lhs: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">, rhs: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">) -> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Bool</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">return</span><span style="font-variant-ligatures:no-common-ligatures"> lhs.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures"> == rhs.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"> </span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">required</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">init</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">_</span><span style="font-variant-ligatures:no-common-ligatures"> value:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span><span style="font-variant-ligatures:no-common-ligatures">) {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">self</span><span style="font-variant-ligatures:no-common-ligatures">.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures"> = value</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures">}</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">class</span><span style="font-variant-ligatures:no-common-ligatures"> Bar:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">override</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">public</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> hashValue: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">return</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures"> * </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">10</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures">}</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">let</span><span style="font-variant-ligatures:no-common-ligatures"> foo = </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">10</span><span style="font-variant-ligatures:no-common-ligatures">)</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">let</span><span style="font-variant-ligatures:no-common-ligatures"> bar = </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">10</span><span style="font-variant-ligatures:no-common-ligatures">)</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(79,129,135)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">(</span><span style="font-variant-ligatures:no-common-ligatures">foo</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">.</span><span style="font-variant-ligatures:no-common-ligatures">hashValue</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">) </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,132,0)">// 10</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(79,129,135)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">(</span><span style="font-variant-ligatures:no-common-ligatures">bar</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">.</span><span style="font-variant-ligatures:no-common-ligatures">hashValue</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">) </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,132,0)">// 100</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">((</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">bar</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">as</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">).</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">hashValue</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">) </span><span style="font-variant-ligatures:no-common-ligatures">// 100 instead of 10</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">foo</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(49,89,93)">==</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">bar</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">) </span><span style="font-variant-ligatures:no-common-ligatures">// true</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(79,129,135)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">(</span><span style="font-variant-ligatures:no-common-ligatures">foo</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">.</span><span style="font-variant-ligatures:no-common-ligatures">hashValue</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> == </span><span style="font-variant-ligatures:no-common-ligatures">bar</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">.</span><span style="font-variant-ligatures:no-common-ligatures">hashValue</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">) </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,132,0)">// false</span></p></div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">As you can see in the above code, although `foo == bar` is true, `foo.hashValue == bar.hashValue` is not guaranteed to be true. As far as I know, Set<T> uses hash values instead of equations to compare the elements. So the results of a super class and its sub class are not guaranteed. Also, as `(bar as Foo).hashValue` is always the result of its own class, you can't get the results you want through casting.</div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif"><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> fooSet:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Set</span><span style="font-variant-ligatures:no-common-ligatures"><</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">> = [</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">10</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">9</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">8</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">7</span><span style="font-variant-ligatures:no-common-ligatures">)]</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> barSet:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Set</span><span style="font-variant-ligatures:no-common-ligatures"><</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">> = [</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">8</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">7</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">6</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">5</span><span style="font-variant-ligatures:no-common-ligatures">)]</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(79,129,135)"><span style="font-variant-ligatures:no-common-ligatures">fooSet</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">subtract</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">(</span><span style="font-variant-ligatures:no-common-ligatures">barSet</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">)</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">fooSet</span><span style="font-variant-ligatures:no-common-ligatures">.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">forEach</span><span style="font-variant-ligatures:no-common-ligatures"> { </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">"</span><span style="font-variant-ligatures:no-common-ligatures">\</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">(</span><span style="font-variant-ligatures:no-common-ligatures">type(of:$0)</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">), value:</span><span style="font-variant-ligatures:no-common-ligatures">\</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">(</span><span style="font-variant-ligatures:no-common-ligatures">$0.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">)"</span><span style="font-variant-ligatures:no-common-ligatures">) }</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures">/*</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures"> Foo, value:10</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures"> Foo, value:9</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures"> Foo, value:8 // Here is a mystery, Foo(7) is </span>unreasonably missing.</p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(79,129,135)">
</p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures">*/</span></p></div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">However, if you can guarantee the hash values are comparable, you still can get the results you want.</div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif"><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(112,61,170)"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">class</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> Foo:</span><span style="font-variant-ligatures:no-common-ligatures">Hashable</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> value: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"> </span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">public</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> hashValue: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">return</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"> </span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">public</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">static</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">func</span><span style="font-variant-ligatures:no-common-ligatures"> ==(lhs: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">, rhs: </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">) -> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Bool</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">return</span><span style="font-variant-ligatures:no-common-ligatures"> lhs.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures"> == rhs.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"> </span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">required</span><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">init</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">_</span><span style="font-variant-ligatures:no-common-ligatures"> value:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Int</span><span style="font-variant-ligatures:no-common-ligatures">) {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">self</span><span style="font-variant-ligatures:no-common-ligatures">.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures"> = value</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> }</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures">}</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;min-height:13px"><span style="font-variant-ligatures:no-common-ligatures"></span><br></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">class</span><span style="font-variant-ligatures:no-common-ligatures"> Bar:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"> </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> name = </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">"bar"</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures">}</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"><br></span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> fooSet:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Set</span><span style="font-variant-ligatures:no-common-ligatures"><</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">> = [</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">10</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">9</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">8</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Foo</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">7</span><span style="font-variant-ligatures:no-common-ligatures">)]</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures">
</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(187,44,162)">var</span><span style="font-variant-ligatures:no-common-ligatures"> barSet:</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(112,61,170)">Set</span><span style="font-variant-ligatures:no-common-ligatures"><</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">> = [</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">8</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">7</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">6</span><span style="font-variant-ligatures:no-common-ligatures">), </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">Bar</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(39,42,216)">5</span><span style="font-variant-ligatures:no-common-ligatures">)]</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures"><br></span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(79,129,135)"><span style="font-variant-ligatures:no-common-ligatures">fooSet</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">subtract</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">(</span><span style="font-variant-ligatures:no-common-ligatures">barSet</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(0,0,0)">)</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">fooSet</span><span style="font-variant-ligatures:no-common-ligatures">.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">forEach</span><span style="font-variant-ligatures:no-common-ligatures"> { </span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(61,29,129)">print</span><span style="font-variant-ligatures:no-common-ligatures">(</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">"</span><span style="font-variant-ligatures:no-common-ligatures">\</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">(</span><span style="font-variant-ligatures:no-common-ligatures">type(of:$0)</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">), value:</span><span style="font-variant-ligatures:no-common-ligatures">\</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">(</span><span style="font-variant-ligatures:no-common-ligatures">$0.</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(79,129,135)">value</span><span style="font-variant-ligatures:no-common-ligatures;color:rgb(209,47,27)">)"</span><span style="font-variant-ligatures:no-common-ligatures">) }</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures">/*</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures"> Foo, value:10</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures"> Foo, value:9</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo"><span style="font-variant-ligatures:no-common-ligatures">
</span></p><p style="margin:0px;font-size:11px;line-height:normal;font-family:menlo;color:rgb(0,132,0)"><span style="font-variant-ligatures:no-common-ligatures">*/</span></p></div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif"><br></div><div class="gmail_default" style="font-family:georgia,serif">Zhaoxin</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 1, 2016 at 8:31 AM, Nick Brook via swift-users <span dir="ltr"><<a href="mailto:swift-users@swift.org" target="_blank">swift-users@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">I have a set, Set<A> and a subset of that, Set<B>, where B: A. I want to subtract Set<B> from Set<A>, but the subtract function signature specifies that the set elements must be the same type (S.Generator.Element == Element). I guess this is because Element is not required to be a class, simply hashable, therefore inheritance is not guaranteed? Is there any way this could be implemented in Set, in an extension, or what would be the most efficient way to perform that operation?<div><br></div><div>Thanks<span class="HOEnZb"><font color="#888888"><br><div>
<br><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;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;display:inline!important;float:none">Nick</span></div></font></span></div></div><br>______________________________<wbr>_________________<br>
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