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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>About the proposed names:</p>
<p>To be crystal clear we could use more descriptive names for our two types. Today <code>T.Type</code> is referred as *metatype* and serving two different purposes at once.</p>
<ol>
<li><p>It’s a concrete type; we call it <code>Type<T></code> or other suggested names looked like <code>ExactType<T></code>, <code>StaticType<T></code> etc.</p></li>
<li><p><code>T.Type</code> is also the <em>base type</em> for all subtypes of <code>T</code>.</p></li>
</ol>
<p>Protocols has one exception here.</p>
<p>1.1. The concrete type for protocols is not <code>T.Type</code> but <code>T.Protocol</code>.</p>
<p>2.1. <code>T.Protocol</code> has only one supertype, which is the existential (#2) <code>Any.Type</code> type.</p>
<p>Our proposal slices this behaviour into two different types, where you only can create a *concrete type* <code>Type<T></code> with <code>T.self</code> or shadow a concrete type behind <code>Subtype<U></code> with <code>subtype(of:)</code> function.</p>
<p>To be precise the correct names should be:</p>
<ul>
<li><code>Metatype<T></code> for the concrete type (#1).</li>
<li><code>ExistentialMetatype<T></code> for the existential type (#2).</li>
</ul>
<p>But we felt that we should adopt the existing name from <code>T.Type</code> and use the short form for the *concrete type* <code>Type<T></code>.</p>
<hr>
<p>Brent already showed in multiple examples but the question seems to come up over and over about the correct name of the current <code>type(of:)</code> function.</p>
<p>Imagine this scenario:</p>
<pre><code class="swift">protocol P {}
struct A : P {}
let proto: P = A()
let any: Any = proto
// the old behaviour looked like this
// *concrete* `A.Type` is hidden behind the existential `Any.Type`
let anyMetatype: Any.Type = any.dynamicType
anyMetatype is P.Type //=> true `P.Type` is the existential type here
anyMetatype is A.Type //=> true
let aMetatype = anyMetatype as! A.Type // Okay
// today `type(of:)` does the same trick
// After this proposal:
// subtype<T>(of instance: T) -> Subtype<T>
// The function will extract `Type<A>` for `any` but shadow it behind `Subtype<Any>`
let anyMetatype: `Subtype<Any>` = subtype(of: any)
// The correct relationship look like this:
// Subtype<P> : Subtype<Any>
// Subtype<A> : Subtype<P>
// Type<A> : Subtype<A>
anyMetatype is Subtype<P> //=> true
anyMetatype is Subtype<A> //=> true
anyMetatype is Type<A> //=> true
anyMetatype is Type<P> //=> false
anyMetatype is Type<Any> //=> false
let aMetatype_1 = anyMetatype as! Subtype<A> // Okay
let aMetatype_2 = anyMetatype as! Type<A> // Okay
</code></pre>
<p><code>subtype(of:)</code> function extracts the *concrete type* from the given instance but shadows it behind the *existential type* equal to the type of the given instance.</p>
<p><code>subtype(of: T)</code> returns a existential metatype instance <code>Subtype<T></code> where in reality it’s a concrete metatype <code>Type<U></code> with the relationship like <code>U : T</code>.</p>
<p>This is exact the same behaviour as the old <code>.dynamicType</code> had.</p>
<p>I hope that cleared some raising questions. </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_1475260675378149888" 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 30. September 2016 um 09:00:53, Goffredo Marocchi 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><span style="color: rgb(0, 0, 0); font-family: 'helvetica Neue', helvetica; font-size: 14px; 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; background-color: rgb(255, 255, 255); display: inline !important; float: none;">Calling it SuperTypeOf<T> and SubTypeOf<T> would make it less confusing as that is how I read it in my mind in your last example.</span></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>