<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="">It seems to me that it isn't very different from:<div class=""><br class=""></div><div class=""><div class=""></div><blockquote type="cite" class=""><div class="">let foo: Int</div><div class="">if someCondition {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>foo = 4</div><div class="">}</div><div class="">// is immutable foo initialized or not, must prevent both reads and writes</div></blockquote><div class=""><br class=""></div><div class="">which is currently handled properly.</div><div class="">
<br class="Apple-interchange-newline"><span style="color: rgb(0, 0, 0); font-family: 'Lucida Grande'; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none;" class="">Félix</span>
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<br class=""><div><blockquote type="cite" class=""><div class="">Le 3 févr. 2016 à 19:45:11, Dany St-Amant via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: LucidaGrande; 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" class=""><div class=""><br class="Apple-interchange-newline">Le 3 févr. 2016 à 19:22, Chris Lattner via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 3, 2016, at 3:00 PM, Félix Cloutier <<a href="mailto:felixcca@yahoo.ca" class="">felixcca@yahoo.ca</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Thanks. I have updated the proposal to reflect this.<div class=""><br class=""></div><div class="">One thing that remains unspecified is the behavior when the closure throws. Feedback and opinions would be very welcome here.</div><div class=""><br class=""></div><div class="">Some alternatives that I can think of:</div><div class=""><br class=""></div><div class=""><ul class="MailOutline"><li class="">disallow throwing from @noescape(once) closures;</li></ul></div></div></div></blockquote><div class=""><br class=""></div><div class="">I’d strongly prefer this. Once/if the base proposal is accepted and implemented, we can always expand from there if strong motivation exists for doing so.</div><div class=""><br class=""></div><div class="">-Chris</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Previously I had thought of the try? and try! but even with plain try the compiler might not know if a variable is initialized or not if the @noescape(once)<span class="Apple-converted-space"> </span><b class="">must not</b><span class="Apple-converted-space"> </span>run on throws</div><div class=""><br class=""></div><div class=""><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="color: rgb(187, 44, 162);">let</span><span class="Apple-converted-space"> </span>foo:<span class="Apple-converted-space"> </span><span class="" style="color: rgb(112, 61, 170);">Int</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="color: rgb(187, 44, 162);">do</span><span class="Apple-converted-space"> </span>{</div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"> <span class="Apple-converted-space"> </span><span class="" style="color: rgb(187, 44, 162);">try</span><span class="Apple-converted-space"> </span>withLock(someLock, timeout:<span class="Apple-converted-space"> </span><span class="" style="color: rgb(39, 42, 216);">0.5</span>) {</div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"> <span class="Apple-converted-space"> </span><span class="" style="color: rgb(79, 129, 135);">foo</span><span class="Apple-converted-space"> </span>= sharedThing.foo</div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"> }</div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);"><span class="" style=""> <span class="Apple-converted-space"> </span></span>// immutable foo can be read not written to</div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);"><span class="" style="">}<span class="Apple-converted-space"> </span></span>catch<span class="" style=""><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(209, 47, 27);"><span class="" style=""> <span class="Apple-converted-space"> </span></span><span class="" style="color: rgb(61, 29, 129);">print</span><span class="" style="">(</span>"couldn't acquire lock fast enough"<span class="" style="">)</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;">}</div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);">// is immutable foo initialized or not, must prevent both reads and writes</div><div class=""><br class=""></div></div><div class="">So will the compiler be able to properly handle this ambiguity?</div><div class=""><br class=""></div><div class="">Dany</div><br class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><br class=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><ul class="MailOutline"><li class="">allow throwing and allow the error to be re-thrown (and force `once` closures to be executed on throwing paths);</li><li class="">return the closure error (possibly incompatible with some function return types).</li></ul><div class=""><br class="Apple-interchange-newline"><span class="" style="font-family: 'Lucida Grande'; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;">Félix</span></div><br class=""><div class=""><blockquote type="cite" class=""><div class="">Le 3 févr. 2016 à 17:18:51, Chris Lattner <<a href="mailto:clattner@apple.com" class="">clattner@apple.com</a>> a écrit :</div><br class="Apple-interchange-newline"><div class=""><blockquote type="cite" class="" style="font-family: LucidaGrande; 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;"><div class=""><br class="Apple-interchange-newline">On Feb 3, 2016, at 1:21 PM, Félix Cloutier <<a href="mailto:felixcca@yahoo.ca" class="">felixcca@yahoo.ca</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">I updated the proposal to address some concerns. It can be found at: <a href="https://github.com/zneak/swift-evolution/blob/master/proposals/00xx-noescape-once.md" class="">https://github.com/zneak/swift-evolution/blob/master/proposals/00xx-noescape-once.md</a><div class=""><br class=""></div><div class="">Things that changed:</div><div class=""><br class=""></div><div class=""><ul class="MailOutline"><li class="">It now says that the closure must be called on code paths where the function throws;</li><li class="">you can have multiple @noescape(once) parameters but they can't make assumptions from one another.</li></ul><div class=""><br class=""></div><div class="">I'm not 100% convinced that forcing a call on code paths that throw is always desirable. I've changed it because Chris's support probably means that the feature has better chances of making it, but I'm not convinced yet.<span class="Apple-converted-space"> </span></div></div></div></div></blockquote><div class="" style="font-family: LucidaGrande; 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;"><br class=""></div><div class="" style="font-family: LucidaGrande; 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;">To be clear, (once) needs to specify either that the closure is guaranteed to be executed on the error path, or that it is guaranteed not to be. I can see the argument that “guaranteed not” is the best default. If you think that is the best way to go, feel free to make that be the proposal. Either way, please mention in “alternatives” that it needs to be one or the other, but could be switched (from whatever you propose) if there is a compelling reason.</div><div class="" style="font-family: LucidaGrande; 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;"><br class=""></div><div class="" style="font-family: LucidaGrande; 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;">-Chris</div><br class="" style="font-family: LucidaGrande; 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;"><blockquote type="cite" class="" style="font-family: LucidaGrande; 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;"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class="">If throwing allows me to return without calling the closure, I can write this:</div><div class=""><br class=""></div><div class=""><div class="">do {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>let foo: Int</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>try withLock(someLock, timeout: 0.5) {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>foo = sharedThing.foo</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>}</div><div class="">} catch {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>print("couldn't acquire lock fast enough")</div><div class="">}</div></div><div class=""><br class=""></div><div class="">which would be kind of messy if instead, the closure needed a parameter to tell whether the lock was acquired or not when it runs.</div><div class=""><div class=""><br class="Apple-interchange-newline"><span class="" style="font-family: 'Lucida Grande'; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;">Félix</span></div></div></div></div></div></blockquote></div></blockquote></div><br class=""></div></div></div></blockquote></div><br class=""></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class="" style="font-family: LucidaGrande; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; 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