<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 Aug 19, 2016, at 18:22, Slava Pestov <<a href="mailto:spestov@apple.com" class="">spestov@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><blockquote type="cite" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;"><div class=""><br class="Apple-interchange-newline">On Aug 19, 2016, at 2:04 PM, Jordan Rose 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 class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="">We have an old Radar about this, <a href="rdar://problem/16754935" class="">rdar://problem/16754935</a>. It's probably just a case we're missing in enum layout. My guess is that it's because we don't have a whole spare bit in a RawPointer, but we should be able to pick some up either from alignment or from ABI knowledge.</div><div class=""><br class=""></div><div class="">Jordan</div></div></div></blockquote><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=""><br class=""></div><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="">Hi Jordan,</div><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=""><br class=""></div><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="">I asked about a related issue, which is that RawPointer only has 1 extra inhabitant instead of 4096. You guys said you wanted non-zero integers to round-trip through RawPointer. It seems that declaring the high bits of a RawPointer as spare bits would cause the same problem as allowing more extra inhabitants.</div><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=""><br class=""></div><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="">Also I don’t think alignment is the answer here, RawPointer should be able to represent a char *, where you have no low spare bits.</div></div></blockquote><br class=""></div><div>Ah, yeah, sorry, I didn't really mean RawPointer here. I do think Builtin.RawPointer should continue to be able to round-trip with Int (except 0) because of the things people do in C. I should have said "known non-tagged object pointer", which has to be a valid address, and which _StringBuffer._Storage certainly should be.</div><div><br class=""></div><div>I dug into this a little, and it looks like we've got this nesting:</div><div><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div>case large(_StringBuffer._Storage)</div><div>typealias _StringBuffer._Storage = _HeapBuffer<_StringBufferIVars, UTF16.CodeUnit></div><div>struct _HeapBuffer<Value, Element> {</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>internal var _storage: Builtin.NativeObject?</div><div>}</div></blockquote><div><br class=""></div><div>So because _HeapBuffer can be empty, we get into trouble. We don't have a _NonEmptyHeapBuffer, but I suppose we could store a _StringBuffer._Storage.Storage instead.</div><div><br class=""></div><div>Jordan</div><br class=""></body></html>