<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 Oct 5, 2017, at 6:34 PM, Jordan Rose via swift-dev <<a href="mailto:swift-dev@swift.org" class="">swift-dev@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div class=""><br class=""><blockquote type="cite" class=""><div class="">On Oct 5, 2017, at 15:23, David Zarzycki <<a href="mailto:dave@znu.io" class="">dave@znu.io</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class="Apple-interchange-newline"><br class=""><blockquote type="cite" class=""><div class="">On Oct 5, 2017, at 18:08, Jordan Rose <<a href="mailto:jordan_rose@apple.com" class="">jordan_rose@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><br class=""><div class=""><br class=""><blockquote type="cite" class=""><div class="">On Oct 5, 2017, at 13:42, David Zarzycki via swift-dev <<a href="mailto:swift-dev@swift.org" class="">swift-dev@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Hello,<br class=""><br class="">As an experiment, I’d like to force the exclusivity checking logic to always error at compile time, rather than a mix of compile time and run time. Near as I can tell, there is no built in debugging logic to do this (not even to warn when dynamic checks are added). Am I missing something? Where would be the best place in the code to make the dynamic checker error/warning at compile time? Would a warning be useful to others? Or should I just keep this on a throwaway branch?<br class=""></div></div></blockquote></div><br class=""><div class="">It's worth noting that this is impossible in the general case:</div><div class=""><br class=""></div><blockquote class="" style="margin: 0px 0px 0px 40px; border: none; padding: 0px;">// Library.swift</blockquote><blockquote class="" style="margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div class="">public class Foo {</div><div class=""> public var x: Int = 0</div><div class=""> public init() {}</div><div class="">}</div><div class="">public func testExclusivity(_ a: Foo, _ b: Foo, by callback: (inout Int, inout Int) -> Void) {</div><div class=""> callback(&a.x, &b.x)</div><div class="">}</div></blockquote><br class=""><blockquote class="" style="margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div class="">// Client.swift, compiled as a separate target</div><div class="">let foo = Foo()</div><div class="">testExclusivity(foo, foo) { $0 = 42; $1 = 8192 }</div></blockquote><div class=""><br class=""></div>That doesn't necessarily mean there aren't improvements to be made, but it might change your goals.</div></div></blockquote></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Hi Jordan,</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Thanks for writing the above code. Just to be clear, are you pointing out that exclusivity checking through opaque code (like a library) is problematic? Or that classes introduce their own aliasing challenges? Or both? Or something else entirely?</div></div></blockquote><div class=""><br class=""></div><div class="">The former, really. Classes are just the most convenient way to get coincidental aliasing.</div></div></div></div></blockquote><div><br class=""></div>The important point here is that the "conservatively emit static errors for every exclusivity check we can't resolve statically" rule is basically equivalent to "disallow mutable class properties", because we do not have any language support for the sort of unique-right-to-access rules that would be necessary to ever resolve any of those statically.</div><div><br class=""></div><div>John.</div><div><br class=""></div><div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class=""><br class=""></div><br class=""><blockquote type="cite" class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">If we set aside resiliency for a second, couldn't the exclusivity checker dynamically crash in the above scenario if two or more InOutExprs end up resolving to the same address? If not, then why not?</div></blockquote><br class=""></div><div class="">"If we set aside resiliency" isn't something that works today. Local builds don't actually have access to the SIL of <i class="">any</i> of their dependencies at the moment (for a handful of reasons). Opaque code really does have to be treated as opaque.</div><div class=""><br class=""></div><div class="">(If this isn't convincing, then consider 'a' and 'b' coming directly from Objective-C code, where there's no exclusivity checking logic at all.)</div><div class=""><br class=""></div><div class="">Jordan</div><br class=""></div>_______________________________________________<br class="">swift-dev mailing list<br class=""><a href="mailto:swift-dev@swift.org" class="">swift-dev@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-dev<br class=""></div></blockquote></div><br class=""></body></html>