<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 Jan 27, 2017, at 11:04, Slava Pestov via swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@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; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">On Jan 27, 2017, at 10:39 AM, tuuranton--- via swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Yes, but why?<div class=""><br class=""><div class="">What's the rationale for this?</div><div class=""><br class=""></div><div class="">What would be so bad about allowing overriding a non-failable initializer with a failable initializer?</div></div></div></div></blockquote><div class=""><br class=""></div>If the non-failable initializer witnesses a non-failable protocol requirement, and the subclass overrides it, what should be the runtime behavior if the subclass initializer returns nil? The caller won’t expect it, since the caller is calling a non-failable initializer.</div></div></blockquote><div><br class=""></div><div>This <i class="">particular</i> objection only applies to 'required' initializers, though.</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><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=""></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="">For similar reasons, you cannot override a method that returns a non-optional value with a method returning an optional value.</div></div></blockquote><br class=""></div><div>Yes, this is true.</div><div><br class=""></div><div>Jordan</div><br class=""></body></html>