<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 class=""><div style="font-family: HelveticaNeue;" class=""><blockquote type="cite" class=""><div class="">On Jun 27, 2016, at 1:17 PM, Douglas Gregor via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><br class=""><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">The <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">LocalizedError</code> protocol describes an error that provides localized messages for display to the end user, all of which provide default implementations. The conforming type can provide implementations for any subset of these requirements:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">protocol</span> LocalizedError <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> Error {
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// A localized message describing what error occurred.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> errorDescription: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span>? { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">get</span> }
…
}
</pre></div></div></div></div></blockquote></div><div class="" style="font-family: HelveticaNeue;"><br class=""></div><div class="" style="font-family: HelveticaNeue;">Given that LocalizedError would now be its own protocol that not all errors would conform to, could errorDescription be non-optional?</div><div class="" style="font-family: HelveticaNeue;"><br class=""></div><div class="" style="font-family: HelveticaNeue;"><blockquote type="cite" class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; word-wrap: normal; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;"> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> errorDescription: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">String</span> { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">get</span> }</pre></div></div></div></blockquote></div><div class="" style="font-family: HelveticaNeue;">It would be nice if conformance to LocalizedError guaranteed the presence of a user-readable message. Such a guarantee is useful when building a UI.</div><div class="" style="font-family: HelveticaNeue;"><br class=""></div><div class="" style="font-family: HelveticaNeue;">I realize the bridging to NSError may make this impossible, but in principle it seems like the right design.</div><div class="" style="font-family: HelveticaNeue;"><br class=""></div><div class="" style="font-family: HelveticaNeue;">Cheers,</div><div class="" style="font-family: HelveticaNeue;"><br class=""></div><div class="" style="font-family: HelveticaNeue;">Paul</div></div></body></html>