C++ Logo

SG12

Advanced search

Subject: Re: [ub] Justification for < not being a total order on pointers?
From: John Spicer (jhs_at_[hidden])
Date: 2013-08-26 12:02:31


On Aug 26, 2013, at 12:12 PM, Nevin Liber <nevin_at_[hidden]> wrote:

> On 26 August 2013 11:00, Jeffrey Yasskin <jyasskin_at_[hidden]> wrote:
>
> Could someone explain why we need to allow operator<(T*) to be a non-order?
>
> It comes from C. I believe it comes from the days of segmented architectures.
>
> I do not know of any modern machines that have such architectures and have C++11 compilers for them. Whenever it comes up for discussion on various reflectors, no one has mentioned one either. I for one would like to see this restriction go away.
>
> Armchair thought: maybe we should propose a total ordering for pointers (for C++17 at this point) and see if anyone objects?
>
>
> All that being said, I believe Library is inconsistent in its use of operator< vs. std::less<T>, and that needs to be addressed separately. Pointers are the current poster child for the issue but user code might be specializing std::less as well.
> --
> Nevin ":-)" Liber <mailto:nevin_at_[hidden]> (847) 691-1404

Given that it is possible to reinterpret_cast a pointer to a large-enough integer and being able to cast back to get the original pointer, it seems like it should be possible to support operator< on pointers.

John.



SG12 list run by herb.sutter at gmail.com