<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=""><span class="Apple-tab-span" style="white-space:pre"> </span>An immediate problem I’m seeing is the error: <span style="font-family: Menlo; font-size: 11px; text-indent: -12px;" class="">using 'Error' as a concrete type conforming to protocol 'Error' is not supported, </span>which means we can’t use Error in our Result or Response types, as both the value and error types are generic there. I’m guessing we’ll have to either remove the generic error type, which would greatly impact consumer’s ability to use our APIs with their own custom errors, or wrap all errors in our own error type, which is terrible for a few reasons. Or just keep using NSError I guess. Any clever solutions here?<div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Jon</div><div class=""> <div><blockquote type="cite" class=""><div class="">On Aug 14, 2016, at 1:41 AM, Jon Shier <<a href="mailto:jon@jonshier.com" class="">jon@jonshier.com</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; -webkit-line-break: after-white-space;" class="">Doug, et. al.:<div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>Thanks for the discussion so far; I think I understand the new error model from a user’s perspective. However, now I’m looking for some guidance for framework developers. While the proposal laid out the system types would wrap imported Objective-C errors, I don’t see anything for the desired patters for Swift native errors. For instance, in Alamofire we currently either pass through the NSErrors we receive from underlying frameworks or generate our own, usually in our own domain, with unique error codes and such. I can see my way to translating most of these directly to an AFError type that conforms to Error, but some of them require associated values (e.g. the content type validation error needs to know the expected and actual content types). In these cases I’m having a hard time see how these things should be stored, especially when only some cases need this data. Of course, I’m away of the LocalizedError protocol, but that doesn’t seem applicable here, as I’m mostly wondering about storage. Rather than creating types similar to the system error types, perhaps a basic enum based error would work, where only the cases that need it capture values? I’m mostly curious what the anticipated pattern was here.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Jon</div><div class=""><br class=""><div class=""><div class=""><blockquote type="cite" class=""><div class="">On Aug 6, 2016, at 1:15 AM, Kevin Ballard 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=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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">On Aug 5, 2016, at 7:36 PM, Erica Sadun <<a href="mailto:erica@ericasadun.com" class="">erica@ericasadun.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><span class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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;">On Aug 5, 2016, at 8:10 PM, Kevin Ballard <</span><a href="mailto:kevin@sb.org" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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;">kevin@sb.org</a><span class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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;">> wrote:</span><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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=""><br class="Apple-interchange-newline"><div class=""><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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=""><div class=""><br class="Apple-interchange-newline">On Aug 5, 2016, at 5:16 PM, Erica Sadun <<a href="mailto:erica@ericasadun.com" class="">erica@ericasadun.com</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;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Aug 5, 2016, at 4:19 PM, Douglas Gregor 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=""><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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=""><div class=""><br class="Apple-interchange-newline">On Aug 5, 2016, at 12:59 PM, Kevin Ballard 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=""><div class=""><div class="">If all you want to do is get the localized description, then you can just say `(error as NSError).localizedDescription`.<br class=""></div></div></div></blockquote><div class=""><br class=""></div>Just ‘error.localizedDescription’ works now. That was part of SE-0112.</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;"><span class="Apple-tab-span" style="white-space: pre;"> </span>- Doug</div></div></blockquote><br class=""></div><div class="">Would it kill to allow:</div><div class=""><br class=""></div><div class="">let err = NSError()</div><div class="">err.localizedDescription = "bad things happen"</div><div class="">throw err</div><div class=""><br class=""></div><div class="">or even</div><div class=""><br class=""></div><div class="">throw NSError("Bad things happen")</div><div class=""><br class=""></div><div class="">for lightweight use? I ended up refactoring entirely to enum : Error because Swift yelled at me for using NSError(): "this results in an invalid NSError instance. It will raise an exception in a future release. Please call errorWithDomain:code:userInfo: or initWithDomain:code:userInfo:. This message shown only once."</div><div class=""><br class=""></div><div class=""><div class="" style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">enum</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>Errors:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Error</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">case</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>bad}</span></div><div class="" style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(79, 129, 135);"><span class="" style="font-variant-ligatures: no-common-ligatures;">Errors</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">bad</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures;">_code</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 132, 0);">// 0</span></div><div class="" style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Errors</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">bad</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">_domain</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">// "Errors"</span></div><div class="" style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Errors</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">bad</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">_userInfo</span><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures;">// Optional({})</span></div><div class="" style="margin: 0px; font-size: 16px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Errors</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">bad</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">localizedDescription</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">// "The operation couldn’t be completed. (Errors error 0.)"</span></div></div><div class=""><br class=""></div>Bleh.</div></div></blockquote><br class=""></div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;">NSErrors need a domain/code. It doesn’t make much sense to throw one without it. And besides, there’s a fairly trivial solution for doing what you want to do:</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;">struct GenericError: LocalizedError {</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;"> let message: String</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;"> init(_ message: String) {</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;"> self.message = message</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;"> var errorDescription: String? {</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;"> return message</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;">Now you can just say `throw GenericError(“Bad things happen”)`.</div><div class="" style="font-family: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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: Palatino-Roman; font-size: 14px; font-style: normal; font-variant-caps: 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;">-Kevin Ballard</div></div></blockquote><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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;">I know I can build workarounds but if we're going to have the error.localizedDescription, making it an initializable/assignable property just seems like a nice thing™. Why can't we have nice things™?</div></div></blockquote></div><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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;">I don’t actually think it’s a nice thing™ to have it be assignable like you ask, because we should be encouraging people to use typed errors. You may as well just ask for String to conform to Error (in fact, you could just add that conformance yourself and skip the GenericError wrapper entirely).</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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;">-Kevin</div><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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="">_______________________________________________</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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-caps: 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="">swift-evolution mailing list</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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=""><a href="mailto:swift-evolution@swift.org" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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="">swift-evolution@swift.org</a><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: 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="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></div></blockquote></div><br class=""></div></div></div></div></blockquote></div><br class=""></div></body></html>