<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Mar 14, 2017, at 1:02 AM, Andrew Thompson 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="">Hello Swift Evolution Community,<br class=""><br class="">I’ve been thinking about a new language feature that would allow properties to be first class citizens. The basic idea is as follows:<br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>let x: PropertySelector<UIView, CGFloat> = #property(UIView.frame.origin.x)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>let view: UIView = …<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>view.frame.origin.x = 20<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>x.read(view) // returns 20<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>x.write(view, value: 9091)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>view.frame.origin.x // now 9091<br class=""><br class="">This is a trivial example, but now we can do more interesting things in our code. For example, we can animate any property on a view (that is documented to be animatable of course):<br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func animate(view: UIView, property: PropertySelector<UIView, CGFloat>, amount: Int) {<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>let originalValue = property.read(view)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>func generateKeyFrames() {<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>let step = 1.0 / Double(amount)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>for i in 0..<amount {<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>let newValue = originalValue + CGFloat(i)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>let time = Double(i) / Double(amount)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>UIView.addKeyframe(withRelativeStartTime: time,<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span> relativeDuration: step,<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span> animations: { property.write(view, value: newValue) }<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>}<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>}<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span>UIView.animateKeyframes(withDuration: 1.0,<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span> delay: 0,<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span> options: [],<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span> animations: generateKeyFrames,<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span><span class="Apple-tab-span" style="white-space:pre"> </span> completion: nil)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>}<br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>let myView: UIView = …<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>myView.frame = CGRect(x: 20, y: 100, width: 99, height: 120)<br class=""><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>// once this completes, myView.frame.origin.x == 120<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>animate(view: myView, property: #property(UIView.frame.origin.x), amount: 100)<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span><br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>// once this completes, myView.frame.size.width == 198<br class=""><span class="Apple-tab-span" style="white-space:pre"> </span>animate(view: myView, property: #property(UIView.frame.size.width), amount: 99)<br class=""><br class="">I think this would be a pretty neat feature to have, what do you think?<br class=""></div></div></blockquote></div><br class=""><div class="">We agree! How does this sound:</div><div class=""><br class=""></div><div class=""><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170313/033998.html" class="">https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170313/033998.html</a></div><div class=""><br class=""></div><div class="">-Joe</div></body></html>