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.error { color:#AA0000; }</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="bloop_markdown"><p>I also thought about the <code>Either</code> type.</p>
<pre><code class="swift">enum Either<A, B> where A != B {
case -> A
case -> B
}
</code></pre>
<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_1488303403552835840" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div> <br><p class="airmail_on">Am 28. Februar 2017 um 18:35:45, Matthew Johnson via swift-evolution (<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div></div><div>
<title></title>
<br class="">
<div>
<blockquote type="cite" class="">
<div class="">On Feb 28, 2017, at 11:33 AM, Joe Groff <<a href="mailto:jgroff@apple.com" class="">jgroff@apple.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<blockquote type="cite" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;" class=""><br class="Apple-interchange-newline">
On Feb 28, 2017, at 9:23 AM, Matthew Johnson <<a href="mailto:matthew@anandabits.com" class="">matthew@anandabits.com</a>> wrote:<br class="">
<br class="">
<br class="">
<blockquote type="cite" class="">On Feb 28, 2017, at 11:04 AM, Joe
Groff via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class="">
<br class="">
<br class="">
<blockquote type="cite" class="">On Feb 27, 2017, at 4:34 PM, Rex
Fenley via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class="">
<br class="">
I often find myself running into situations where I'll receive
"Ambiguous use of..." for overloaded functions or operators. In
every case these situations would be easily solved if I could
specify "Generic != CertainType" in the where clause of one of the
overloads so I can disambiguate the cases. Could this be added to
language?<br class=""></blockquote>
<br class="">
Do you have a concrete example where you need this? It'd be good to
know whether the types are ambiguous due to type checker bugs, or
whether there's a principle by which they could be naturally
ordered. Instead of overloading, can you do the type test via `if
!(x is CertainType)` within a single implementation?<br class=""></blockquote>
<br class="">
The best use case I can think of is if we had enum cases where the
associated value is a subtype of the enum:<br class="">
<br class="">
enum Result<T, E> where E: Error, T != E {<br class="">
case some(T) -> T<br class="">
case error(E) -> E<br class="">
}<br class=""></blockquote>
<br 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="">
<span 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; float: none; display: inline !important;" class="">I don't think that's a good design for that type. I can
see the desire for a subtype relationship between T and
Result<T, E>, but no good reason for the error to also be a
subtype. That != constraint would have to be propagated through
anything using `Result<T, E>` as well.</span><br 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=""></div>
</blockquote>
<div><br class=""></div>
<div>Ok, just change it to a fully generic Either type then.
I’m not arguing for or against this constraint, just pointing
out a use case that is enabled by it. It’s reasonable to
argue that we don’t want to support this use case.</div>
<br class="">
<blockquote type="cite" class="">
<div class=""><br 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="">
<span 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; float: none; display: inline !important;" class="">-Joe</span></div>
</blockquote>
</div>
<br class="">
_______________________________________________<br>swift-evolution mailing list<br>swift-evolution@swift.org<br>https://lists.swift.org/mailman/listinfo/swift-evolution<br></div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>