<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 15 Aug 2016, at 20:39, Xiaodi Wu 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 dir="ltr" style="font-family: Helvetica; font-size: 12px; 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;" class=""><div class="gmail_extra"><div class="gmail_quote">On Mon, Aug 15, 2016 at 2:29 PM, Tim Vermeulen<span class="Apple-converted-space"> </span><span dir="ltr" class=""><<a href="mailto:tvermeulen@me.com" target="_blank" class="">tvermeulen@me.com</a>></span><span class="Apple-converted-space"> </span>wrote:<br class=""><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><br class=""><div class=""><div class=""><div class="h5"><blockquote type="cite" class=""><div class="">On 15 Aug 2016, at 21:27, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" target="_blank" class="">xiaodi.wu@gmail.com</a>> wrote:</div><br class=""><div class=""><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote">On Mon, Aug 15, 2016 at 1:57 PM, Haravikk via swift-evolution<span class="Apple-converted-space"> </span><span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span><span class="Apple-converted-space"> </span>wrote:<br class=""><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><br class=""><div class=""><span class=""><blockquote type="cite" class=""><div class="">On 15 Aug 2016, at 13:44, Tim Vermeulen <<a href="mailto:tvermeulen@me.com" target="_blank" class="">tvermeulen@me.com</a>> wrote:</div><br class=""><div class=""><div class=""><blockquote type="cite" class=""><blockquote type="cite" class="">On 15 Aug 2016, at 08:02, Justin Jia via swift-evolution<<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolutio<wbr class="">n@swift.org</a>(<a href="mailto:swift-evolution@swift.org" target="_blank" class="">mailto:swift-<wbr class="">evolution@swift.org</a>)>wrote:<br class="">Hi!<br class=""><br class="">I don’t know if this has came up before. I tried to search though the mailing list but didn’t find any related threads.<br class=""><br class="">This is purely a syntactic thing (which I know it’s the lowest priority for Swift 4), but I think it’s an important one.<br class=""><br class="">Let’s say we have a struct with a function:<br class=""><br class="">```<br class="">struct Foo {<br class="">func bar(x: Int)<br class="">}<br class="">```<br class=""><br class="">We can use optionals:<br class=""><br class="">```<br class="">let foo: Foo? = nil<br class="">let x = 1<br class="">foo!.bar(x: x) // Able to compile, but will cause runtime error<br class="">foo?.bar(x: x) // Able to compile, and won't cause runtime error<br class="">```<br class=""><br class="">However:<br class=""><br class="">```<br class="">let foo = Foo()<br class="">let x: Int? = nil<br class="">foo.bar(x: x!) // Able to compile, but will cause runtime error<br class="">foo.bar(x: x?) // Won't compile<br class="">```<br class=""><br class="">I propose that we should allow `foo.bar(x: x?)`, which should be equivalent to:<br class=""><br class="">```<br class="">if let x = x {<br class="">foo.bar(x: x)<br class="">}<br class="">```<br class=""><br class="">What do you think?<br class=""></blockquote>I like the intent behind this, but personally I think it's not clear enough. For me, putting the statement in a conditional as you've shown is the better solution, as it's a lot clearer exactly what's going on. Putting a question mark on a variable makes it look like something specific to that variable, rather than preventing the entire statement from executing.<br class=""></blockquote><br class="">I get where you’re coming from, but how would people react if optional chaining wasn’t in the language yet and someone proposed it now? I know it’s not strictly the same thing, but it’s still a single question mark that prevents the whole statement from being executed. I think it would be met with a lot of resistance from people saying that being more explicit with `if let` is the way to go.<br class=""></div></div></blockquote><div class=""><br class=""></div></span><div class="">True, but with optional chaining the position of the question mark makes it a lot more clear where it stops, whereas in this proposal the question mark seems a bit less intuitive since it's within the parenthesis yet affecting the statement outside of it.</div><span class=""><br class=""><blockquote type="cite" class=""><div class=""><div class=""><blockquote type="cite" class="">There may be some alternatives though, for example, what about a shorthand for the conditional like so:<br class=""><br class="">if let x? { foo.bar(x: x) }<br class="">if x? { foo.bar(x: x) } // even shorter?<br class=""></blockquote><br class="">The alternatives you’ve come up with would only work if foo.bar doesn’t return anything. If it does return something, and you want to assign it to a variable, you have to declare the variable beforehand and it just becomes ugly. It’s then probably a better idea to use map/flatmap:</div></div></blockquote></span></div><br class=""><div class="">Hmm, what about something involving the where keyword? Something like:</div><div class=""><br class=""></div><blockquote style="margin: 0px 0px 0px 40px; border: none; padding: 0px;" class=""><div class=""><font face="Monaco" class="">let value = foo.bar(x: x) where x?</font></div></blockquote><br class=""><div class="">Some people have queried the ability to use where in assignments before, as another way to have a statement be nil if a condition isn't met, but in this case the condition is that x is unwrapped (thus valid for the call). This basically lets you use it like a "retroactive" conditional, it'd be nice to get the same x? behaviour on for loops anyway (letting you unwrap values that way, and maybe test them too).</div></div></blockquote><div class=""><br class=""></div><div class="">`let value = (x == nil) ? nil : foo.bar(x: x)` isn't so bad, is it?</div></div></div></div></div></blockquote><div class=""><br class=""></div></div></div><div class="">In my opinion, it is.</div></div></div></blockquote><div class=""><br class=""></div><div class="">It certainly isn't much longer, and its meaning is clear to anyone with a basic grasp of Swift. What makes it bad, in your opinion?</div><div class=""> </div><blockquote class="gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204); padding-left: 1ex;"><div style="word-wrap: break-word;" class=""><div class=""><div class="">And you’d even need to write `foo.bar(x: x!)`, right?</div></div></div></blockquote><div class=""><br class=""></div><div class="">You would. That's my bad.</div></div></div></div></div></blockquote><br class=""></div><div>Forgot about the ternary conditional!</div><div>For the force unwrapping, that's something that could be avoided in future by type narrowing; just as we currently can't do:</div><div><br class=""></div><div><font face="Monaco" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>if value is String { value.somethingUniqueToString() } // Must cast first or use if let value = value as? String</font></div><div><br class=""></div><div>Doing the same for optionality would allow force unwrapping to be removed in future; I find having to use force unwrapping when I know I don't need to annoying, but it's hardly much of an inconvenience to be sure of what's going on.</div></body></html>