<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 Dec 31, 2015, at 4:26 PM, Kevin Ballard <<a href="mailto:kevin@sb.org" class="">kevin@sb.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">On Thu, Dec 31, 2015, at 01:40 PM, Michel Fortin wrote:</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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="">Le 30 déc. 2015 à 16:40, Kevin Ballard via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :<br class=""><blockquote type="cite" class="">On Wed, Dec 30, 2015, at 01:33 PM, Joe Groff wrote:<br class=""><blockquote type="cite" class="">Another possibility I've thought of is defining `defer { val }` to guarantee that val remains alive until the defer fires on scope exit. That might let us leave `defer` as the one "guarantee something happens exactly at scope exit" language construct.<br class=""></blockquote><br class="">Oh that's cute. I'd probably want to say `defer { _ = val }` though, to make it obvious that this is intentional.<br class=""></blockquote><br class="">Or you could make it even more obvious what this is by giving that feature a name. For instance:<br class=""><br class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>defer { _fixLifetime(val) }<br class=""><br class="">The good thing about this one is that it already works, because that's what `withExtendedLifetime` does internally. Also, if you search a bit, you'll end up here with a nice explanation of what that function does.<br class=""><a href="https://github.com/apple/swift/blob/8d9ef80304d7b36e13619ea50e6e76f3ec9221ba/stdlib/public/core/LifetimeManager.swift#L45" class="">https://github.com/apple/swift/blob/8d9ef80304d7b36e13619ea50e6e76f3ec9221ba/stdlib/public/core/LifetimeManager.swift#L45</a><br class=""><br class="">So why not simply remove the underscore?<br class=""></blockquote><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">Because it's not a very good API? Having some magic function called `fixLifetime()` that keeps values alive is a little weird. `withExtendedLifetime()` is also slightly weird, but it makes more sense than fixLifetime() does, since withExtendedLifetime() is the specific solution to the problem of "I need to ensure this value remains alive for this entire scope because reasons".</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">I'd much rather just see the syntax `_ = val` be converted into `Builtin.fixLifetime(val)` because the only reason to write an expression like that is because you want to make sure the value is still alive at that point (that and because it's not unreasonable for people to assume that `_ = val` will keep the value alive, so it would be nice to make that assumption actually be correct).</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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></blockquote></div><br class=""><div class="">I don't think this is obviously true. `val` could be a computed property you just want to force the side effects for. (Computed properties with side effects maybe aren't a great idea, but there are some in AppKit/UIKit.)</div><div class=""><br class=""></div><div class="">-Joe</div></body></html>