<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 Apr 16, 2017, at 10:42 AM, Xiaodi Wu 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=""><span 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; float: none; display: inline !important;" class="">The point is that, when you manipulate two real numbers, sometimes there is no numeric result. You cannot simply wish this away with a new numeric type because it is not an artifact of _modeling_ real numbers but rather intrinsic to mathematics itself.</span></div></blockquote></div><br class=""><div class="">I agree with the rest of what you said, but I have to disagree on this point. What I think he is saying is that, in Swift, we really should be representing the NaN case as an optional instead of a magic value on the type itself (similar to how swift uses an optional instead of NSNotFound).</div><div class=""><br class=""></div><div class="">In fact, that might be an actual option here. For ‘Double?’ the compiler could use the bit pattern for NaN internally to represent .none (I believe it does similar tricks to save space with other optional types). Then disallow reference to NaN within swift code. Functions or operations which could produce NaN would either have to produce an optional or trap in case of NaN. (e.g. the trig functions would likely return an optional, and 0/0 would trap).</div><div class=""><br class=""></div><div class="">I think it would actually lead to much better code because the compiler would force you to have to explicitly deal with the case of optional/NaN when it is possible. Migration would be tricky though...</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Jon</div></body></html>