[ub] Canonical ordering

Nevin Liber nevin at eviloverlord.com
Fri Oct 18 19:12:58 CEST 2013


On 18 October 2013 01:46, Christopher Jefferson <chris at bubblescope.net>wrote:

> Here is a suggestion. How about we make the result of comparing pointers
> from different allocations into implementation-defined behaviour?
>
While it gets it out of this group, I don't think that addresses the real
problem.

Of course, if you think that:

bool isInArray = std::begin(a) <= p && p < std::end(a);

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:

bool isInArray = static_cast<bool>(p);

(possibly even 'isInArray = true;', but I'd have to study the rules for
nullptrs to see if this is allowed)

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...
-- 
 Nevin ":-)" Liber  <mailto:nevin at eviloverlord.com>  (847) 691-1404
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.open-std.org/pipermail/ub/attachments/20131018/05d281e9/attachment.html 


More information about the ub mailing list