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.send { color:#77bb77; }
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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>We had similar talks about that topic before. There is a thread somewhere on this, but it’s mainly focused on value type semantics.</p>
<p>If I remember correctly we might even discussed to remove the <code>class</code> constraint completely from the language and introduce a protocol solution to this problem. </p>
<p>There are also some words about the <code>class</code> constraint in the <a href="https://github.com/apple/swift/blob/611fc78d28a5da97dd1bea40761b913b1077aef5/docs/GenericsManifesto.md#generalized-class-constraints">GenericsManifesto.md</a></p>
<blockquote>
<h3 id="generalizedclassconstraints">Generalized <code>class</code> constraints</h3>
<p>The <code>class</code> constraint can currently only be used for defining protocols. We could generalize it to associated type and type parameter declarations, e.g.,</p>
<pre><code class="Swift">protocol P {
associatedtype A : class
}
func foo<T : class>(t: T) { }
</code></pre>
<p>As part of this, the magical <code>AnyObject</code> protocol could be replaced with an existential with a class bound, so that it becomes a typealias:</p>
<pre><code class="Swift">typealias AnyObject = protocol<class>
</code></pre>
<p>See the “Existentials” section, particularly “Generalized existentials”, for more information.</p>
</blockquote>
<ul>
<li><p>Instead of <code>: class</code> we might use <code>: AnyObject</code> as a constraint (or <code>: AnyReference</code>?).</p></li>
<li><p>Instead of <code>: struct/enum</code> we should have something like <code>: value</code> or even better <code>: AnyValue</code>.</p></li>
</ul>
<hr>
<p>I believe we should focus on existential types first before fixing this gap in Swift. <code>Any<T></code> might receive the mentioned constraints and could create something like this:</p>
<pre><code class="swift">typealias AnyObject = Any<class>
typealias AnyValue = Any<value>
</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_1477037505090391040" 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 21. Oktober 2016 um 08:55:40, Xiaodi Wu 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><div></div><div>
<title></title>
What's your use case for distinguishing structs and enums?<br>
<div class="gmail_quote">
<div dir="ltr">On Fri, Oct 21, 2016 at 1:40 AM Mike Kasianowicz via
swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>
wrote:<br></div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr" class="gmail_msg">Currently protocols can have the
class constraint:
<div class="gmail_msg">protocol MyProtocol : class {}<br class="gmail_msg"></div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">It would be (a) intuitive and (b) useful to
allow such things as:</div>
<div class="gmail_msg">protocol Model : struct {} or protocol Event
: enum {}</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">These types of restrictions can help prevent
accidental anti-patterns or misuse of APIs.</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">Seems simple and non-controversial...
right?</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">[Note: I'd like to see even more
heavy-handed protocol restrictions in the future. For
example, a protocol describing an enum with a common case, or a
struct with no reference members. Great stuff for defensively
coding APIs.]</div>
</div>
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</blockquote>
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