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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>It’s probably the influence from iOS development where I have delegate protocols like this one:</p>
<pre><code class="swift">@objc public protocol _ContainerViewControllerDelegate: class {
@objc optional func containerViewController(_ containerViewController: ContainerViewController,
willPerform operation: ContainerViewController.Operation,
from oldViewController: UIViewController,
to newViewController: UIViewController,
animated: Bool)
@objc optional func containerViewController(_ containerViewController: ContainerViewController,
didPerform operation: ContainerViewController.Operation,
from oldViewController: UIViewController,
to newViewController: UIViewController,
animated: Bool)
@objc optional func containerViewController(_ containerViewController: ContainerViewController,
willSet oldViewControllers: [UIViewController],
to newViewControllers: [UIViewController],
animated: Bool)
@objc optional func containerViewController(_ containerViewController: ContainerViewController,
didSet newViewControllers: [UIViewController],
from oldViewControllers: [UIViewController],
animated: Bool)
}
</code></pre>
<p>Implementing noops for each function in an extension seems kind of a wrong decision for a few reasons:</p>
<ul>
<li><p>They don’t make sense, because either the receiver implements a function or not. So optional functions provide a more natural solution to that problem.</p></li>
<li><p>We don’t have to pass unnecessarily any arguments to the top functions.</p></li>
<li><p>(Personal preference) I tend to avoid <code>@objc</code> in general. </p></li>
</ul>
<p>I think there was some technical reason why we don’t have <code>optional</code> functions in pure Swift yet, something that also affects <code>dynamic</code> if I’m not mistaken.</p>
<p>Think of the protocol from above as of an existential of a set of functions. The problem is that, I don’t want to introduce a standalone protocol for every function, so the client can decide which protocol it will conform to to avoid these noops. Furthermore, it’s way easier to check for an optional function in your control flow instead of dealing with default values delegate functions with a more complex return type might have.</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_1490683816095092992" 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 28. März 2017 um 07:31:50, Slava Pestov (<a href="mailto:spestov@apple.com">spestov@apple.com</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>
<br class="">
<div>
<blockquote type="cite" class="">
<div class="">On Mar 27, 2017, at 1:48 PM, Adrian Zubarev via
swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="bloop_markdown" style="font-family: Helvetica, Arial; font-size: 13px; 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-stroke-width: 0px; background-color: rgb(254, 254, 254);">
<ul style="margin: 15px 0px;" class="">
<li style="margin: 15px 0px; -webkit-margin-before: 0px;" class="">
<p style="margin: 15px 0px; -webkit-margin-before: 0px;" class="">
Assuming we’ll get that functionality, both<span class="Apple-converted-space"> </span><code style="font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(234, 234, 234); margin: 0px 2px; padding: 0px 5px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;" class="">var</code><span class="Apple-converted-space"> </span>and<span class="Apple-converted-space"> </span><code style="font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(234, 234, 234); margin: 0px 2px; padding: 0px 5px; word-break: normal; word-wrap: normal;" class="">let</code><span class="Apple-converted-space"> </span>should satisfy the protocol
requirements right?</p>
</li>
</ul>
</div>
</div>
</blockquote>
In theory, there’s no reason not to allow that.</div>
<div><br class="">
<blockquote type="cite" class="">
<div class="bloop_markdown" style="font-family: Helvetica, Arial; font-size: 13px; 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-stroke-width: 0px; background-color: rgb(254, 254, 254);">
<ul style="margin: 15px 0px;" class="">
<li style="margin: 15px 0px;" class="">
<p style="margin: 15px 0px; -webkit-margin-before: 0px;" class="">
If it is valid, could we potentially get optional functions in pure
Swift as well?</p>
<div class=""><br class=""></div>
</li>
</ul>
</div>
</blockquote>
I mean, you can already do this:</div>
<div><br class=""></div>
<div>protocol P {</div>
<div> var optionalRequirement: ((Int) -> ())? { get
}</div>
<div>}</div>
<div><br class=""></div>
<div>extension P {</div>
<div> // “default implementation"</div>
<div> var optionalRequirement: ((Int) -> ())? { return nil
}</div>
<div>}</div>
<div><br class=""></div>
<div>struct A : P {}</div>
<div><br class=""></div>
<div>struct B : P {</div>
<div> let optionalRequirement: ((Int) -> ())? = { (x: Int)
in print(x) }</div>
<div>}</div>
<div><br class=""></div>
<div>But it’s kind of tacky.</div>
<div><br class=""></div>
<div>If you think about it, “optional requirement” is an oxymoron.
What’s your use-case?</div>
<div><br class=""></div>
<div>Slava</div>
</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>