Re: [boost] [container] [flat_map] Sub-optimal behavior when utilized with std::less<>

Subject: Re: [boost] [container] [flat_map] Sub-optimal behavior when utilized with std::less<>
From: Viktor Sehr (viktor.sehr_at_[hidden])
Date: 2018-06-15 12:20:15

Hi Andrey,
Thanks for looking it up! I hope it gets merged into 1.68.

/Viktor

On Fri, Jun 15, 2018 at 1:50 PM Andrey Semashev via Boost <
boost_at_[hidden]> wrote:

> On 06/15/18 13:22, Viktor Sehr via Boost wrote:
> > It seems to me that neither boost::flat_map nor boost:flat_set with a
> > custom comparator such as std::less<> behaves like std::set/std::map.
> > This results in unnecessary allocation, in difference from std::map/set
> > when used with a std::string as key for example
> >
> > Example:
> > // Please note that I pretend that "dummy" is large enough to make the
> > std::string utilize the heap.
> > auto set = std::set<std::string, std::less<> >{};
> > auto n = set.count("dummy"); // No conversion from const char* to
> > std::string
> >
> > auto flatset = boost::container::flat_set<std::string, std::less<> >{};
> > auto n = flatset.count("dummy"); // const char* is converted to a
> > std::string before comparison, thus resulting in an unnecessary
> allocation.
> >
> > Is this a known issue intended to be resolved?
>
> Support for templated lookup methods have been added not long ago.
>
> https://github.com/boostorg/container/issues/69
>
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