<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="">In my opinion, simple left to right evaluation where it short circuits on the first failure is the simplest. But I don’t think it matters that much as long as we have a consistent way to define it, and explain it.<div class=""><br class=""></div><div class="">It is nice to have forward transfer from other features, but sometimes we just need to forge ahead to create something new and then have education on the new feature.</div><div class=""><br class=""><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 11, 2017, at 11:28 AM, 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="">This topic has been discussed at least two and maybe more times in the past. It’s hard for me to post links at the moment, but it should be possible to find on Google.<br class=""><br class="">One major challenge to this idea, for which no satisfactory answer has been achieved after all these years, is the following issue:<br class=""><br class=""> f(g()?, h()?, i(), j()?)?<br class=""><br class="">If g() evaluates to nil, is h() called or not? How about i(), which is not failable? Since any function or property access can have side effects, in what order are the arguments evaluated, and how does one reason about this code flow?<br class=""><br class="">To my mind, in the absence of an intuitive answer to the above—which does not appear to be possible—this idea is not feasible.<br class=""><div class="gmail_quote"><div dir="ltr" class="">On Mon, Dec 11, 2017 at 12:34 Magnus Ahltorp via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br class="">
> 12 Dec. 2017 02:58 Jared Khan <<a href="mailto:jaredkhan@me.com" target="_blank" class="">jaredkhan@me.com</a>> wrote:<br class="">
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> 2. It felt natural to me. It’s analogous to the existing optional chaining scenarios and composes nicely. I think it’s about as understandable as existing chaining, a newbie would have to look it up to discover its meaning. What are your thoughts on this particular syntax (ignoring 3. momentarily)? Hopefully others in this thread can share their views too.<br class="">
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Chaining methods is linear, while nesting fills a similar purpose when we use function calls. This of course affects the way existing Swift code is written, but that is something we have to live with if we want to use familiar syntax patterns. However, I think we have to consider this difference in this case, since the syntax becomes more convoluted. Your suggestion is definitely not as easy to read as the optional chaining syntax, and maybe it can't be.<br class="">
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> As for how common I’d expect it to be, it’s something I’ve run into myself a few times. Again, I hope members of this list can give their view on if this would be useful to them.<br class="">
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I don't have any real examples, but I certainly think that I have run into it, so I'm quite open to solving the problem. For me, it is probably only a matter of finding a syntax that is acceptable.<br class="">
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> 3. I’m not entirely sure what the grammar situation is yet but afaik ‘?’ has never been available as a postfix operator. Perhaps I’m missing your point, could you demonstrate where it is allowed?<br class="">
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I did not expect that you would be able to answer that, it was more a question directed to people who are more connected to the inner workings of the parsing of Swift than I am. It is not allowed, but the error message is not the one I expect, something that gives me a hint that it does have some meaning early in the parsing.<br class="">
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/Magnus<br class="">
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