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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"><blockquote>
<p>what if OneOf<A, A>?</p>
<p>duplicate variable compile warning?</p>
</blockquote>
<p>I already answered that question:</p>
<blockquote>
<blockquote>
<p>For example:</p>
<p>typealias ABC = A | B | C</p>
<p>typealias ABCD = ABC | D</p>
<p>we just use an existed type ABC to construct ABCD</p>
<p>But how about generic wrap?</p>
</blockquote>
<p>Bikeshedding:</p>
<pre><code class="swift">// we generate the boundary with `A | B` or directly OneOf<A, B>
enum OneOf<...T> {
...case $#(T)
// Bikeshedding variadic enum casses:
// we might need an index to set the value?
init(index: Int, value: T) {
self = .$index(value)
}
}
/// Usage:
/// A | B | C == OneOf<A, B, C>
func |<T, U>(_: T.Type, _: U.Type) -> OneOf<T, U>.Type {
// I also use the proposal to remove `.self` magic here
return OneOf<T, U>
}
// Here is how to merge OneOf into a single dimension
func |<...T, U>(_: OneOf<...T>.Type, _: U.Type) -> OneOf<...T, U>.Type {
// Copy and merge types into the new `OneOf` type
return OneOf<...T, U>
}
func |<T, ...U>(_: T.Type, _: OneOf<...U>.Type) -> OneOf<T, ...U>.Type {
// Copy and merge types into the new `OneOf` type
return OneOf<T, ...U>
}
func |<...T, ...U>(_: OneOf<...T>.Type, _: OneOf<...U>.Type) -> OneOf<...T, ...U>.Type {
// Copy and merge types into the new `OneOf` type
return OneOf<...T, ...U>
}
</code></pre>
<p>Your example will become:</p>
<pre><code class="swift">typealias ABC = A | B | C // or OneOf<A, B, C>
typealias ABCD = ABC | D // merging lhs OneOf with D to OneOf<A, B, C, D>
</code></pre>
<p>Mission accomplished.</p>
<p><strong>Again this is not a true union type because <code>String | String</code> != <code>String</code></strong></p>
</blockquote>
<p>You’d get a OneOf enum with both first and second case as <code>A</code>. You still can distinguish them by the indexed label.</p>
<pre><code class="swift">let test = OneOf<A, A>.init(index: 0, value: A())
switch test {
case .$1(let value)
// do something
case .$2(let value)
// do something
}
</code></pre>
<p>Again this is all bikeshedding of variadic generics and variadic enums!</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_1467379460018212096" 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 1. Juli 2016 um 11:08:40, Cao Jiannan 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>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
<div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">
<div class="">
<div class="">Hi all,</div>
<div class=""><br class=""></div>
<div class="">I'm now officially proposal the union type feature
for Swift. Please see:</div>
<div class=""><br class=""></div>
<br class="Apple-interchange-newline">
<a href="https://github.com/frogcjn/swift-evolution/blob/master/proposals/xxxx-union-type.md" class="">https://github.com/frogcjn/swift-evolution/blob/master/proposals/xxxx-union-type.md</a></div>
<div class="">
<h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);">
Introduction</h2>
<p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">
Add union type grammar, represents the type which is one of other
types.</p>
<div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">
<pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> stringOrURL: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">|</span> URL <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span><a href="https://www.apple.com/" class="">https://www.apple.com</a><span class="pl-pds" style="box-sizing: border-box;">"</span></span></pre></div>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
<div class="">I would be thankful if someone support this idea and
give some advice. Thanks!</div>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
<div class="">--</div>
</div>
<div class="">Jiannan</div>
</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>