<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="">+1 for trapping unless using &==. In the case of ‘Float?’ we could also map to nil.<div class=""><br class=""></div><div class="">This is probably a more appropriate discussion for evolution though...<br class=""><div class=""><div class=""><br class=""></div><div class=""><br class=""><div class=""><div><blockquote type="cite" class=""><div class="">On Oct 19, 2017, at 9:48 PM, Brent Royal-Gordon via swift-dev <<a href="mailto:swift-dev@swift.org" class="">swift-dev@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; line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class="">On Oct 19, 2017, at 4:29 PM, Xiaodi Wu via swift-dev <<a href="mailto:swift-dev@swift.org" class="">swift-dev@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="">D) Must floating-point IEEE-compliant equivalence be spelled `==`?</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=""><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="">In my view, this is something open for debate. I see no reason why it cannot be migrated to `&==` if it were felt that `==` *must* be a full equivalence relation. I believe this is controversial, however.</div></div></blockquote><br class=""></div><div class="">I actually got partway through writing up a pitch on this yesterday, but my opinion is that NaNs are so exceptional, and so prone to misuse, that we ought to treat them like integer arithmetic overflows: trap when they're detected, unless you use an `&` variant operator which indicates you know what you're doing.</div><div class=""><br class=""></div><div class="">I strongly suspect that, in practice, most float-manipulating code is not prepared to handle NaN and will not do anything sensible in its presence. For example, Apple platforms use floating-point types for geometry, color components, GPS locations, etc. Very little of this code will do anything sensible in the presence of a NaN. Arguably, it'd be better to exclude them through the type system, but I don't think that's a realistic possibility—we would need to have done that in a more source-break-friendly era. But that doesn't have to mean we're completely stuck.</div><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; border-spacing: 0px;"><div class=""><div style="font-size: 12px; " class="">-- </div><div style="font-size: 12px; " class="">Brent Royal-Gordon</div><div style="font-size: 12px; " class="">Architechies</div></div></span>
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