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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>First of all, writing CRTP is already allowed in Swift, however it doesn’t work at all. </p>
<p>For example one would assume that the output of the following code sample might look like this <code>1 2 3 4</code>:</p>
<pre><code class="swift">print(1)
class Template<T> {}
class RealThing : Template<RealThing> {
override init() { print(2) }
func foo() { print(3) }
}
let instance = RealThing()
instance.foo()
print(4)
</code></pre>
<p>However the result is only <code>1</code> and your application will simply stuck at that point without crashing or throwing any bad runtime error.</p>
<p><a href="https://bugs.swift.org/browse/SR-2549">https://bugs.swift.org/browse/SR–2549</a></p>
<p>I discovered an API in UIKit which uses that pattern, obviously it’s written in Objective-C but it is imported in Swift and it actually works, because it’s not pure swift.</p>
<pre><code class="swift">// Generic superclass
open class NSLayoutAnchor<AnchorType : AnyObject> : NSObject { ... }
// Non-generic subclasses with the `Sub : Super<Sub>` pattern
open class NSLayoutXAxisAnchor : NSLayoutAnchor<NSLayoutXAxisAnchor> {}
open class NSLayoutYAxisAnchor : NSLayoutAnchor<NSLayoutYAxisAnchor> {}
open class NSLayoutDimension : NSLayoutAnchor<NSLayoutDimension> { ... }
</code></pre>
<p>My questions are:</p>
<ul>
<li>Will we ever allow this in Swift?</li>
<li>Does CRTP bring any technical improvement to Swifts generic system?</li>
<li>Is it something for Swift 4 to consider?</li>
<li>Does it need a proposal or should we only see it as a bug?</li>
</ul>
<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_1487875318105079040" 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></body></html>