<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
        {font-family:"Cambria Math";
        panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
        {font-family:Calibri;
        panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
        {font-family:"Calisto MT";
        panose-1:2 4 6 3 5 5 5 3 3 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
        {margin:0in;
        margin-bottom:.0001pt;
        font-size:12.0pt;
        font-family:"Times New Roman","serif";}
a:link, span.MsoHyperlink
        {mso-style-priority:99;
        color:blue;
        text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
        {mso-style-priority:99;
        color:purple;
        text-decoration:underline;}
p
        {mso-style-priority:99;
        mso-margin-top-alt:auto;
        margin-right:0in;
        mso-margin-bottom-alt:auto;
        margin-left:0in;
        font-size:12.0pt;
        font-family:"Times New Roman","serif";}
span.apple-style-span
        {mso-style-name:apple-style-span;}
span.il
        {mso-style-name:il;}
span.EmailStyle20
        {mso-style-type:personal-reply;
        font-family:"Calisto MT","serif";
        color:#7030A0;}
.MsoChpDefault
        {mso-style-type:export-only;
        font-family:"Calibri","sans-serif";}
@page WordSection1
        {size:8.5in 11.0in;
        margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
        {page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">Not all implementation-defined behavior are created equal;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">I am unsure what the implementation-defined nature of char<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">signed a signed type or not has to do with this.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">I do confess that I don’t believe that piece of code is what<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">should be driving the decision. Why array, and not containers<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">which are general and more widespread? Is it just because the<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">novice is using array? If yes, then the answer to that particular question<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calisto MT","serif";color:#7030A0">is: don’t use array – which is a sound advice to novices anyway.<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-family:"Calisto MT","serif";color:#7030A0"><o:p> </o:p></span></a></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> ub-bounces@open-std.org [mailto:ub-bounces@open-std.org]
<b>On Behalf Of </b>Nevin Liber<br>
<b>Sent:</b> Friday, October 18, 2013 10:13 AM<br>
<b>To:</b> WG21 UB study group<br>
<b>Subject:</b> Re: [ub] Canonical ordering<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">On 18 October 2013 01:46, Christopher Jefferson <<a href="mailto:chris@bubblescope.net" target="_blank">chris@bubblescope.net</a>> wrote:<o:p></o:p></p>
<div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<p>Here is a suggestion. How about we make the result of comparing pointers from different allocations into implementation-defined behaviour?<o:p></o:p></p>
</blockquote>
<div>
<p class="MsoNormal">While it gets it out of this group, I don't think that addresses the real problem.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Of course, if you think that:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"><span class="apple-style-span"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#500050">bool isInArray = </span></span><span class="il"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#222222;background:#FFFFCC">std</span></span><span class="apple-style-span"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#500050">::</span></span><span class="il"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#222222;background:#FFFFCC">begin</span></span><span class="apple-style-span"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#500050">(a)
<= p && p < </span></span><span class="il"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#222222;background:#FFFFCC">std</span></span><span class="apple-style-span"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#500050">::</span></span><span class="il"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#222222;background:#FFFFCC">end</span></span><span class="apple-style-span"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#500050">(a);</span></span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222">is an unreasonable piece of code, there are no problems. :-) If you think it is reasonable, I don't see how making it implementation-defined behavior stops the optimizer from
rewriting that as:<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222">bool isInArray = static_cast<bool>(p);<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222">(possibly even 'isInArray = true;', but I'd have to study the rules for nullptrs to see if this is allowed)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:#222222">And developers can't count on implementation-defined behavior in portable code. Look at all the pain people go through because C didn't nail down (for valid reasons at the time)
the signness of char. And the implementation-defined behavior of the representation of char only has two possible outcomes...<o:p></o:p></span></p>
</div>
</div>
</div>
<p class="MsoNormal">-- <br>
Nevin ":-)" Liber <mailto:<a href="mailto:nevin@eviloverlord.com" target="_blank">nevin@eviloverlord.com</a>>
<a href="tel:%28847%29%20691-1404" target="_blank">(847) 691-1404</a> <o:p></o:p></p>
</div>
</div>
</div>
</div>
</body>
</html>