On Thu, 29 May 2025 at 15:48, Jonathan Wakely <jwak...@redhat.com> wrote:
>
> On Thu, 29 May 2025 at 15:42, Tomasz Kaminski <tkami...@redhat.com> wrote:
> >
> >
> >
> > On Thu, May 29, 2025 at 3:56 PM Patrick Palka <ppa...@redhat.com> wrote:
> >>
> >> Tested on x86_64-pc-linux-gnu, does this look OK for trunk/15?
> >>
> >> -- >8 --
> >>
> >> Instead of effectively doing a zipped comparison of the keys and values,
> >> compare them separately to leverage the underlying containers' optimized
> >> equality implementations.
> >>
> >> libstdc++-v3/ChangeLog:
> >>
> >> * include/std/flat_map (_Flat_map_impl::operator==): Compare
> >> keys and values separately.
> >> ---
> >> libstdc++-v3/include/std/flat_map | 5 ++++-
> >> 1 file changed, 4 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/libstdc++-v3/include/std/flat_map
> >> b/libstdc++-v3/include/std/flat_map
> >> index c0716d12412a..134307324190 100644
> >> --- a/libstdc++-v3/include/std/flat_map
> >> +++ b/libstdc++-v3/include/std/flat_map
> >> @@ -873,7 +873,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >> [[nodiscard]]
> >> friend bool
> >> operator==(const _Derived& __x, const _Derived& __y)
> >> - { return std::equal(__x.begin(), __x.end(), __y.begin(),
> >> __y.end()); }
> >> + {
> >> + return __x._M_cont.keys == __y._M_cont.keys
> >> + && __x._M_cont.values == __y._M_cont.values;
> >
> > Previously we supported containers that do not have operator==, by calling
> > equal.
>
> Oh, good point.
> Using == means the element types of the underlying containers must be
> equality comparable, but the original approach of using std::equal on
> the zipped values only means those tuples must be equality comparable,
> and an evil user could have overloaded:
>
> bool operator==(const tuple<int, MyVal>&, const tuple<int, MyVal>&);
Or const tuple<const int&, const MyVal&>& or whatever the zipped type is.
>
> so that those comparisons work, but MyVal might not be equality comparable.
>
> > For the flat_set we also do not compare the containers. I would suggest
> > using in both:
> > ranges::equal(x._M_cont)
> > Or using == on containers in both flat_map and flat_set.
> >>
> >> + }
> >>
> >> template<typename _Up = value_type>
> >> [[nodiscard]]
> >> --
> >> 2.50.0.rc0
> >>
