<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Are you sure that your problem is about generics on lambdas? Seems to me that you wouldn't need generic lambdas if you could solve your initial problem in a different way.</div><div class=""><br class=""></div>You can use Self in protocols, which refers to the implementing type:<div class=""><br class=""></div><div class=""><div class=""></div><blockquote type="cite" class=""><div class="">protocol MyProtocol {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var protocolControllerCallback: Self -> Void { get }</div><div class="">}</div><div class=""><br class=""></div><div class="">class MyController: MyProtocol {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var protocolControllerCallback: MyController -> Void</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>init() {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>protocolControllerCallback = { cnt in return }</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div class="">}</div></blockquote><div class=""><br class=""></div>That doesn't work right now because Swift will complain that the class must be `final` for reasons that sound bogus to me: "it uses 'Self' in a non-parameter, non-result type position". I don't know if there's a technical reason that it can't be in a closure parameter. Still seems to get you closer to what you want.</div><div class=""><div class="">
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<br class=""><div><blockquote type="cite" class=""><div class="">Le 15 janv. 2016 à 05:07:06, Spencer Kohan via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">New here, hope I'm doing this right.
<div class=""><br class=""></div><div class="">I recently found a use case which does not appear to be covered by the swift language: it appears that there's no way to declare a closure type with generic arguments.</div><div class=""><br class=""></div><div class="">For example, what if I'm building an iOS app, and I want to define a closure which operates on UIViewControllers which implement a particular protocol?<br class=""></div><div class=""><br class=""></div><div class="">In ObjectiveC, this would be possible with the following syntax:</div><div class=""><br class=""></div><div class=""> typedef void (^MyBlockType)(UIViewController<MyProtocol>)</div><div class=""><br class=""></div><div class="">In Swift you can do this in the context of a function, class or struct:</div><div class=""><br class=""></div><div class=""> func myFunction<T: UIViewController where T:MyProtocol>() {</div><div class=""> let x : (T) -> () = { generic in</div><div class=""> ....</div><div class=""> }</div><div class=""> }</div><div class=""><br class=""></div><div class="">But what if you want to declare such a closure as a variable within the protocol it's referring to?</div><div class=""><br class=""></div><div class=""> protocol MyProtocol {</div><div class=""> var protocolControllerCallback : (protocolController : ???? )->()</div><div class=""> }</div><div class=""><br class=""></div><div class="">It seems like Associated Types are the intended tool for this job, so you could have something like:</div><div class=""><br class=""> protocol MyProtocol {</div><div class=""> typealias ProtocolObservingController</div><div class=""> var protocolControllerCallback : (protocolController : ProtocolObservingController )->() {get set}</div><div class=""> }</div><div class=""><br class=""></div><div class=""> class MyController : UIViewController, MyProtocol {</div><div class=""> typealias ProtocolObservingController = MyController</div><div class=""> ...</div><div class=""> }</div><div class=""><br class=""></div><div class="">But this doesn't quite solve the problem: we still can't have a closure defined in this protocol which can operate on *any* implementations of the protocol. For instance, what if we wanted to pass a closure between two different implementations?</div><div class=""><br class=""></div><div class=""> class MyChildController : UIViewController, MyProtocol {</div><div class=""> typealias ProtocolObservingController = MyChildController</div><div class=""> ...</div><div class=""> }</div><div class=""><br class=""></div><div class=""><div class=""> class MyParentController : UIViewController, MyProtocol {</div><div class=""> typealias ProtocolObservingController = MyParentController</div><div class=""> ...</div><div class=""><br class=""></div><div class=""> func createChildController() -> MyControllerChild {</div><div class=""> let child = MyChildController()</div><div class=""> child.protocolControllerCallback = self.protocolControllerCallback</div><div class=""> }</div><div class=""><br class=""></div><div class=""> }</div></div><div class=""><br class=""></div><div class="">It doesn't work because the types of protocolControllerCallback are inconsistent between the two classes.</div><div class=""><br class=""></div><div class="">This feels like a hole in the language.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div></div>
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