<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 Dec 23, 2016, at 2:02 PM, Xiaodi Wu <<a href="mailto:xiaodi.wu@gmail.com" class="">xiaodi.wu@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">I don't currently have a use for it, but I can certainly see how this might be useful to some people.<div class=""><br class=""></div><div class="">As a side note, though, it seems like the consensus is that the optimization shown in your specific example, which is provided by std::vector<bool> in C++, is now widely regarded as a poor design choice. See, for instance, <<a href="http://stackoverflow.com/questions/17794569/why-is-vectorbool-not-a-stl-container" class="">http://stackoverflow.com/questions/17794569/why-is-vectorbool-not-a-stl-container</a>>, <<a href="https://isocpp.org/blog/2012/11/on-vectorbool" class="">https://isocpp.org/blog/2012/11/on-vectorbool</a>>, and <<a href="http://www.gotw.ca/publications/N1211.pdf" class="">http://www.gotw.ca/publications/N1211.pdf</a>>.</div><div class=""><br class=""></div><div class="">It would be interesting to see if you can come up with a use case where the proposed feature is a clear win as opposed to just having a totally separate type that makes clear it's not quite the same thing under the hood (in your example, something like `BitArray`).</div></div></div></blockquote><br class=""></div><div>I'm starting to think my original motivation might’ve had something to do with normally needing storage for both some property <i class="">and</i> a T, but not needing (local) storage for said property if T conformed to a protocol which itself already required conforming types to have that property? Or maybe as a way to have the “bottom” variable in a hierarchy of wrapper types to break the “reference cycle” for some property? (Come to think of it, those could be the same thing)</div><div><br class=""></div><div>That was (and is) an odd project... Anyway, it's been a while since I've thought about it. I'll try to find time today to poke through some old code and see if still have a copy of what I’d gotten stuck on.</div><div><br class=""></div><div>And thanks for those links :-)</div><div><br class=""></div><div>- Dave Sweeris</div></body></html>