<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 Feb 22, 2017, at 1:22 PM, David Sweeris 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 style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">On Feb 22, 2017, at 12:21 PM, Huon Wilson <<a href="mailto:huon@apple.com" class="">huon@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 22, 2017, at 10:20, David Sweeris 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 class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;">What if we extended that to any type that’s ExpressibleByNilLiteral & Equatable?</span></div></blockquote></div><br class=""><div class="">Note that this is not how the Unsafe*Pointer optimization works: in that case, the type Unsafe*Pointer is not ExpressibleByNilLiteral, it just has some spare/guaranteed-to-be-unused sentinel values in its representation, that the compiler knows about. This also works for types like `enum X { case A, B }`: an optional like X? (and X??, all the way up to 254 ?’s) is also represented as a single byte, because there’s spare values that the compiler knows won't be used by valid instances of X.</div><div class=""><br class=""></div><div class="">Converting valid instances to .none would break round-tripping: Optional(x)! would sometimes fail, if x was the sentinel value. This seems likely to cause generic code to stop working.</div></div></div></blockquote><div class=""><br class=""></div><div class="">Oh, hey, yeah, good point! I should’ve thought about that bit more first. Would a `HasInvalidBitPattern` protocol work? </div></div></div></blockquote><div><br class=""></div><div>This is basically how the optional payload optimization works behind the scenes. It’s not specific to optional, or having a certain payload type, it works for other enums also.</div><div><br class=""></div><div>IRGen knows for each builtin type, what the valid and invalid bit patterns are. Basically reference types and unsafe pointers are the ones that are known to have invalid bit patterns (nulls, and for references, we also know the least significant 3 bits are always zero because of alignment). From this it can compute the valid and invalid bit patterns of tuple types and structs that appear in enum payloads also.</div><div><br class=""></div>Slava</div><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; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class=""><div class="" style="margin: 0px; line-height: normal;"><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">protocol</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>HasInvalidBitPattern {</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures;">/// An unreachable bit pattern. Very Bad Things are very likely to happen if this represents a valid value.</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">static</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">var</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>invalidBitPattern:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">Self</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">get</span><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="color: rgb(0, 132, 0); font-variant-ligatures: no-common-ligatures;">// probably use some private init to create this, or some other mechanism that doesn’t get exposed to the client</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;">Then, the special-case Optional definition would be:</span></div><div class=""><span class="" style="font-variant-ligatures: no-common-ligatures;"><div class="" style="margin: 0px; line-height: normal;"><font face="Menlo" class=""><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">enum</span><span class="" style="font-variant-ligatures: no-common-ligatures;"> Optional<T> :<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">ExpressibleByNilLiteral</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">where</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>T: HasInvalidBitPattern & Equatable {</span></font></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal; color: rgb(0, 132, 0);"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">case</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>some(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">)</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">init</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>value:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) {<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>= .</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">some</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(value) }</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">init</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(nilLiteral: ()) {<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>= .</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">some</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">invalidBitPattern</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) }</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="color: rgb(0, 132, 0); font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="color: rgb(187, 44, 162); font-variant-ligatures: no-common-ligatures;">var</span><span class="" style="color: rgb(0, 132, 0); font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">case</span><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span>none: (matches: <span class="" style="color: rgb(112, 61, 170); font-variant-ligatures: no-common-ligatures;">Bool</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, associatedValue:<span class="Apple-converted-space"> </span></span><span class="" style="color: rgb(112, 61, 170); font-variant-ligatures: no-common-ligatures;">Void</span><span class="" style="font-variant-ligatures: no-common-ligatures;">) {</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">switch</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">case</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(49, 89, 93);">some</span><span class="" style="font-variant-ligatures: no-common-ligatures;">(let value):<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(187, 44, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>(value<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(61, 29, 129);">==</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(79, 129, 135);">invalidBitPattern</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, ())</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> }</span></div><div class="" style="font-family: Menlo; margin: 0px; line-height: normal;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="font-family: Menlo;"><br class=""></div></span></div></div></div><blockquote type="cite" class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="">Example program for the enum optimization:</div><div class=""><br class=""></div><div class=""><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">enum</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>X {</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">case</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>A, B</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O2<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">??</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O4<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O2</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O2</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O8<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O4</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O4</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O16<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O8</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O8</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O32<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O16</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O16</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O64<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O32</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O32</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O128<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O64</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O64</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O256<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O128</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O128</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O254<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O128</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O64</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O32</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O16</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O8</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O4</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O2</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>>>>>>></span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">typealias</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>O255<T> =<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">O254</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>?</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">func</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>size<T>(</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">_</span><span class="" style="font-variant-ligatures: no-common-ligatures;">:<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.Type) -><span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">Int</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>{</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> <span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">return</span><span class="" style="font-variant-ligatures: no-common-ligatures;"><span class="Apple-converted-space"> </span>MemoryLayout<</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">T</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>.size</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">}</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;"><span class="" style="font-variant-ligatures: no-common-ligatures;"></span><br class=""></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;">print(size(X.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">),<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 132, 0);">// 1</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> size((X?).</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">),<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 132, 0);">// 1</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> size(O254<</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">X</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">),<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 132, 0);">// 1</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> size(O255<</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">X</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">),<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 132, 0);">// 2</span></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><span class="" style="font-variant-ligatures: no-common-ligatures;"> size(O256<</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(112, 61, 170);">X</span><span class="" style="font-variant-ligatures: no-common-ligatures;">>.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(186, 45, 162);">self</span><span class="" style="font-variant-ligatures: no-common-ligatures;">))<span class="Apple-converted-space"> </span></span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(0, 132, 0);">// 3</span></div></div><div class="" style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><div class="" style="font-family: Helvetica; font-size: 12px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px;">(The last is 3 because the compiler currently essentially treats O255<X> like an opaque/all-values-valid 2-byte type, like Int16, and so adds an extra byte for the extra ?. It could theoretically be 2 if the unused values in the extra byte in O255<X> are reused.)</div></div></div></blockquote></div><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">That’s quite interesting, thanks!</div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div><div class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;">- Dave Sweeris</div><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">_______________________________________________</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">swift-evolution mailing list</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><a href="mailto:swift-evolution@swift.org" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">swift-evolution@swift.org</a><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></div></blockquote></div><br class=""></body></html>