https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108827
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:4a6f3676e7dd9e73a822f4da634b037299f0d482 commit r14-3293-g4a6f3676e7dd9e73a822f4da634b037299f0d482 Author: Patrick Palka <ppa...@redhat.com> Date: Thu Aug 17 12:40:04 2023 -0400 libstdc++: Convert _RangeAdaptorClosure into a CRTP base [PR108827] Using the CRTP idiom for this base class avoids bloating the size of a pipeline when adding distinct empty range adaptor closure objects to it, as detailed in section 4.1 of P2387R3. But it means we can no longer define its operator| overloads as hidden friends, since it'd mean each instantiation of _RangeAdaptorClosure introduces its own distinct set of hidden friends. So e.g. for the outer | in x | (views::reverse | views::join) ADL would find 6 distinct hidden operator| friends: two from _RangeAdaptorClosure<_Reverse> two from _RangeAdaptorClosure<_Join> two from _RangeAdaptorClosure<_Pipe<_Reverse, _Join>> but we really only want to consider the last two. We avoid this issue by instead defining the operator| overloads at namespace scope alongside _RangeAdaptorClosure. This should be fine because the only types defined in this namespace are _RangeAdaptorClosure, _RangeAdaptor, _Pipe and _Partial, so we don't have to worry about unintentional ADL. Reviewed-by: Jonathan Wakely <jwak...@redhat.com> PR libstdc++/108827 libstdc++-v3/ChangeLog: * include/std/ranges (__adaptor::_RangeAdaptorClosure): Convert into a CRTP class template. Move hidden operator| friends into namespace scope and adjust their constraints. (__closure::__is_range_adaptor_closure_fn): Define. (__closure::__is_range_adaptor_closure): Define. (__adaptor::_Partial): Adjust use of _RangeAdaptorClosure. (__adaptor::_Pipe): Likewise. (views::_All): Likewise. (views::_Join): Likewise. (views::_Common): Likewise. (views::_Reverse): Likewise. (views::_Elements): Likewise. (views::_Adjacent): Likewise. (views::_AsRvalue): Likewise. (views::_Enumerate): Likewise. (views::_AsConst): Likewise. * testsuite/std/ranges/adaptors/all.cc: Reinstate assertion expecting that adding empty range adaptor closure objects to a pipeline doesn't increase the size of a pipeline.
