On Thu, 13 Mar 2025 at 06:50, Florian Weimer <fwei...@redhat.com> wrote:
>
> * François Dumont:
>
> > + // Get hash code for a node that comes from another _Hashtable.
> > + // Reuse a cached hash code if the hash function is stateless,
> > + // otherwise recalculate it using our own hash function.
> > + __hash_code
> > + _M_hash_code_ext(const __node_value_type& __from) const
> > + {
> > + if constexpr (__and_<__hash_cached, is_empty<_Hash>>::value)
> > + return __from._M_hash_code;
> > + else
> > + return this->_M_hash_code(_ExtractKey{}(__from._M_v()));
> > + }
>
> Does C++ support stateful hash functions? I don't think so, and I don't
> see it documented as a GNU extension, either.
It does, yes. That's why the hash function isn't required to be
default constructible, and has to be stored in the container and why
doing swap on two containers has to swap the hash functions as well.
