<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br><br>Sent from my iPad</div><div><br>On Jun 30, 2017, at 12:24 AM, Brent Royal-Gordon via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8"><div><blockquote type="cite" class=""><div class="">On Jun 27, 2017, at 10:16 AM, Erica Sadun 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=""><meta http-equiv="Content-Type" content="text/html charset=us-ascii" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Using an operator to provide feedback on the context of a failed unwrap has become a commonly implemented approach in the Swift developer Community. What are your thoughts about adopting this widely-used operator into the standard library?</div><div class=""><br class=""></div><div class=""><font face="Menlo" class="">guard !lastItem.isEmpty else { return }</font></div><div class=""><font face="Menlo" class="">let lastItem = array.last !! "Array must be non-empty"</font></div><div class=""><br class=""></div><div class="">Details here: <a href="https://gist.github.com/erica/423e4b1c63b95c4c90338cdff4939a9b" class="">https://gist.github.com/erica/423e4b1c63b95c4c90338cdff4939a9b</a></div><div class=""><br class=""></div><div class="">Thank you for your thoughtful feedback, -- E</div></div></div></blockquote><br class=""></div><div>Finally found a few minutes to read this thread.</div></div></blockquote><div><br></div>Thanks for your thoughts Brent. I generally agree.<div><br><blockquote type="cite"><div><div><br class=""></div><div>I'm a big fan of the `Never`-based approach. (I was before, but I am more so now.) Here are the points I can see in its favor:</div><div><br class=""></div><div>1. It is extremely clear about what's happening—`!!` is another random operator to learn, but `fatalError(_:)` or `preconditionFailure(_:)` are fairly self-explanatory, and `??` is something you might already be using.</div><div><br class=""></div><div>2. It allows you to control the optimization behavior by using `fatalError`, `preconditionFailure`, or `assertionFailure` as desired.</div><div><br class=""></div><div>3. If we later change `throw` from being a statement to being a `Never`-returning expression, you could use `throw` on the right-hand side of `??`.</div></div></blockquote><div><br></div><div>What do you have in mind here? <span style="background-color: rgba(255, 255, 255, 0);">I don't recall any discussion of `throw` return Never. It seems like a novel use of a bottom type that might preclude the possibility of ever having a Result type that seamlessly bridges to Swift's error handling. </span></div><br><blockquote type="cite"><div><div><br class=""></div><div>4. It supports other `Never`-returning operations, like `abort()` or `exit(_:)` or your custom `usage()` function, on the right side of `??`.</div><div><br class=""></div><div><div>5. It supports file-and-line error reporting without having to add any new features; `!!` could not do this because an operator can't have extra, defaulted parameters to carry the file and line.</div><div class=""><br class=""></div></div><div>6. It harmonizes with the eventual idea of making `Never` a universal bottom type, but we don't actually have to implement that today, because we can just overload `??` for now.</div><div><br class=""></div><div>Against these advantages, the only one I can see for `!!` is that it is terse. Terseness is good, especially for a feature which is competing with the single-character postfix `!` operator, but I can't help but be drawn to the flexibility and power of `??` with a `Never` expression on the right-hand side.</div><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; border-spacing: 0px;"><div class=""><div style="font-size: 12px; " class="">-- </div><div style="font-size: 12px; " class="">Brent Royal-Gordon</div><div style="font-size: 12px; " class="">Architechies</div></div></span>
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