Re: [boost] Interval Library and comparison operators

From: Peter Dimov (pdimov_at_[hidden])
Date: 2002-09-06 07:28:17

From: "David Abrahams" <dave_at_[hidden]>
> From: "Sylvain Pion" <pion_at_[hidden]>
>
> > There is currently in the code a commented specialization of std::less
> for
> > interval.  We need to decide what do with this thing.

Please don't specialize std::less. :-)

> There are arguments which say it's undefined behavior to specialize
> std::less so that it does anything other than x < y.

Another, more practical, argument is that if you specialize std::less, this
will work:

std::set< interval > s;

std::vector< interval > v;
std::sort(v.begin(), v.end(), less<interval>());

but this (for example) will not:

std::set< std::pair<interval, int> > s2;

std::vector< interval > v;
std::sort(v.begin(), v.end());

std::less<> is just a function object "alias" of operator<.

So if you want sets of intervals to work (without an explicit comparator),
provide an operator< that is a strict weak ordering.