<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br><br><div>Regards</div>(From<span class="Apple-style-span" style="-webkit-tap-highlight-color: rgba(26, 26, 26, 0.296875); -webkit-composition-fill-color: rgba(175, 192, 227, 0.230469); -webkit-composition-frame-color: rgba(77, 128, 180, 0.230469); "> mobile)</span></div><div><br>On Jul 18, 2016, at 9:04 AM, Adrian Zubarev via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><style>
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.error { color:#AA0000; }</style><div class="bloop_markdown"><p>This is something <strong>additional</strong>, but I’m curios about how the community feels about it.</p>
<p>I recently come across the issue where conforming to <code>Hashable</code> wasn’t enough to thecke if two instances of the same <em>generic</em> type were equal.</p>
<p>I had additionally provide myself the <code>!=</code> function.</p>
<pre><code class="swift">public func !=<T, U>(lhs: SomeTypeName<T>, rhs: SomeTypeName<U>) -> Bool {
return lhs.hashValue != rhs.hashValue
}
</code></pre>
<p>I wondered if Swift can ever get generic specialization like this:</p>
<pre><code class="swift">public func !=<T : Hashable, U, V>(lhs: T<U>, rhs: T<V>) -> Bool {
return !(lhs.hashValue == rhs.hashValue)
}
</code></pre>
</div></div></blockquote><div>I am not sure about the ordering... Interestingly enough, this is real code written last week as part of a framework:</div><div><br></div><div>Export function newSataStore<T extends DataStore<U>, U> (ctor: { new (config:DataStoreConfig):T, config:DataStoreConfig):T {</div><div> return new ctor(config)</div><div>}</div><div><br></div><div>And this is legal code just to try:</div><div><br></div><div><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> interface Hashable {</span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> getHash(): number<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">}<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">interface T extends Hashable { }<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">class SomeTypeName<Type extends Hashable> {<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> public getHash():number {<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> return ...;<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> }<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> public type():this {<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> return Type;<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> }<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">}<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">function compare<T1 extends T, T2 extends T>(lhs:SomeTypeName<T1>, rhs:SomeTypeName<T2>):boolean {<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> return lhs.getHash() != rhs.getHash();<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);">}<o:p></o:p></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"> </span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;">but this is more interesting:</p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;">type List<T> = T & { next: List<T> } // listObj.next.next.next.???</p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><span style="background-color: rgba(255, 255, 255, 0);"><br></span></p><p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><br></p></div><div><br></div><br><blockquote type="cite"><div><div class="bloop_markdown"><p>This function in stdlib would fill the gap. Or we need an extra protocol <code>GenericHashable</code> which includes <code>!=</code>.</p>
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div><br><div id="bloop_sign_1468824857525882880" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div></div><div class="bloop_markdown"><p></p></div></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>swift-evolution mailing list</span><br><span><a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a></span><br><span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br></div></blockquote></body></html>