| Message ID | 20240821125737.3140462-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
On Wed, 21 Aug 2024 at 13:58, Patrick Palka wrote: > > Tested on x86_64-pc-linux-gnu, does this look OK for trunk? I'm not > sure if the current specification of 'projected' strictly speaking > allows for this optimization, but it seems like a natural one that > should be allowed. Yeah, I can't see any conformance problems with doing this. I'm sure somebody smarter than me will point it out if there's a problem, so let's try it and see. OK for trunk, thanks. > > -- >8 -- > > Algorithms that are generalized to take projections usually default the > projection to std::identity, which really means no projection at all. > In that case, I believe we could shortcut the projection logic to return > the indirectly readable type unchanged rather than a wrapped version of > it. This should help with compile times especially after P2609R3 which > made the indirect invocability concepts more expensive to check when > projections are in the picture. > > libstdc++-v3/ChangeLog: > > * include/bits/iterator_concepts.h (__detail::__projected): > Define partial specialization for a std::identity projection. > --- > libstdc++-v3/include/bits/iterator_concepts.h | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h > index d849ddc32fc..642c709fee0 100644 > --- a/libstdc++-v3/include/bits/iterator_concepts.h > +++ b/libstdc++-v3/include/bits/iterator_concepts.h > @@ -803,6 +803,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > using __projected_Proj = _Proj; > }; > }; > + > + // Optimize the common case of the projection being std::identity. > + template<typename _Iter> > + struct __projected<_Iter, identity> > + { using __type = _Iter; }; > } // namespace __detail > > /// [projected], projected > -- > 2.46.0.267.gbb9c16bd4f >
diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h index d849ddc32fc..642c709fee0 100644 --- a/libstdc++-v3/include/bits/iterator_concepts.h +++ b/libstdc++-v3/include/bits/iterator_concepts.h @@ -803,6 +803,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION using __projected_Proj = _Proj; }; }; + + // Optimize the common case of the projection being std::identity. + template<typename _Iter> + struct __projected<_Iter, identity> + { using __type = _Iter; }; } // namespace __detail /// [projected], projected