<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 25, 2016, at 10:30 PM, Charlotte Angela Tortorella 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=""><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=""><div class=""></div><blockquote type="cite" class=""><div class=""> Not a replacement for the Swift 4 source stability goal.</div></blockquote><div class=""><br class=""></div>Swift 4 doesn't actually have a source stability goal. It has an ABI stability goal. These are two very different things. ABI is the calling conventions of the language.</div></div></blockquote><br class=""></div><div>Hi Charlotte,</div><div><br class=""></div><div>Swift 4 has a strong source level compatibility goal. This is explained in the main swift-evolution page and also in the proposal template:</div><div><a href="https://github.com/apple/swift-evolution/blob/master/0000-template.md" class="">https://github.com/apple/swift-evolution/blob/master/0000-template.md</a></div><div><br class=""></div><div>"Relative to the Swift 3 evolution process, the source compatibility requirements for Swift 4 are much more stringent: we should only break source compatibility if the Swift 3 constructs were actively harmful in some way, the volume of affected Swift 3 code is relatively small, and we can provide source compatibility (in Swift 3 compatibility mode) and migration.”</div><div><br class=""></div><div>I agree with you that a migrator could handle this change, but such a significant source breaking change still needs major justification for doing so. Further in the Swift 3 timeframe, this very topic was hotly debated by the folks who wanted to turn the if statement into an expression (eliminating the need for the ?: operator).</div><div><br class=""></div><div>-Chris</div></body></html>