<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 May 14, 2017, at 11:44 PM, André Videla 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=""><blockquote type="cite" class="">Joe also referred to the following model in a thread about Typed Throws.<br class=""><br class=""> () -> () == () throws Never -> ()<br class=""> () throws -> () == () throws Error -> ()<br class=""></blockquote>That makes sense! As a bottom type it would be perfectly fit for this.<br class=""><br class=""><blockquote type="cite" class="">On 15 May 2017, at 03:01, Robert Widmann <<a href="mailto:devteam.codafi@gmail.com" class="">devteam.codafi@gmail.com</a>> wrote:<br class=""><br class="">Though our type lattice doesn’t necessarily have a bottom in the way you’re looking for, you can use Never-returning functions to inhabit a combinator that will do this for you.<br class=""></blockquote>Very useful.<br class="">What do you think of [] as [Never], or nil as Optional<Never>. Can the current inference and subtyping rules deal with that? <br class=""></div></div></blockquote><div><br class=""></div><div>If you mean does this currently compile:</div><div><br class=""></div><div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">let f:Optional<Never> = nil</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="font-variant-ligatures: no-common-ligatures" class="">let g:[Never] = []</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><br class=""></div></div>then yes. However, “nil” and “[]” in the above are literals, not types or type instances. They only are used to initialize an instance of a type that is ExpressibleByNilLiteral / ExpressibleByArrayLiteral.</div><div><br class=""></div><div>If Never becomes a bottom type, a [Never] or Never? hypothetically could be passed into any function which accepts an array or optional of any type because of covariance and value types, but would always be empty/none version of that type. I can’t think of a practical reason to do this, although I admit I’ve never used a language with a bottom type.</div><div><br class=""></div><div>-DW</div></body></html>