On Thu, 11 Jan 2024, Jonathan Wakely wrote:
> On Wed, 10 Jan 2024 at 21:40, Patrick Palka <ppa...@redhat.com> wrote:
> >
> > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> >
> > -- >8 --
> >
> > This avoids redundant moves when composing and partially applying range
> > adaptor objects.
> >
> > Note that the new constraints on _Partial's constructor templates are
> > needed so that it's not inadvertently chosen over the copy constructor
> > when constructing a _Partial object from a non-const _Partial lvalue.
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/std/ranges (views::__adaptor::operator|): Perform
> > perfect forwarding of arguments.
> > (views::__adaptor::_Partial::_Partial): Likewise.
> > (views::__adaptor::_Pipe::__Pipe): Likewise.
> > ---
> > libstdc++-v3/include/std/ranges | 65 ++++++++++++++++++++-------------
> > 1 file changed, 39 insertions(+), 26 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/std/ranges
> > b/libstdc++-v3/include/std/ranges
> > index 81a857502e3..0734daa42bf 100644
> > --- a/libstdc++-v3/include/std/ranges
> > +++ b/libstdc++-v3/include/std/ranges
> > @@ -957,8 +957,11 @@ namespace views::__adaptor
> > requires __is_range_adaptor_closure<_Lhs>
> > && __is_range_adaptor_closure<_Rhs>
> > constexpr auto
> > - operator|(_Lhs __lhs, _Rhs __rhs)
> > - { return _Pipe<_Lhs, _Rhs>{std::move(__lhs), std::move(__rhs)}; }
> > + operator|(_Lhs&& __lhs, _Rhs&& __rhs)
> > + {
> > + return _Pipe<decay_t<_Lhs>, decay_t<_Rhs>>{std::forward<_Lhs>(__lhs),
> > + std::forward<_Rhs>(__rhs)};
> > + }
> >
> > // The base class of every range adaptor non-closure.
> > //
> > @@ -1004,10 +1007,12 @@ namespace views::__adaptor
> > {
> > tuple<_Args...> _M_args;
> >
> > - constexpr
> > - _Partial(_Args... __args)
> > - : _M_args(std::move(__args)...)
> > - { }
> > + template<typename... _Ts>
> > + requires (sizeof...(_Ts) == sizeof...(_Args))
>
> Do we also need a !same_as constraint here? If sizeof...(_Args) == 1
> then this could be chosen instead of a constructor, no?
For the == 1 case we would have used a different partial specialization
of _Partial (one that doesn't use heavyweight std::tuple). So checking
sizeof...(_Ts) == sizof...(_Args) instead is sufficient and simpler.
Checking sizeof...(_Args) > 1 would be sufficient as well.
>
> Or is
> > + constexpr
> > + _Partial(_Ts&&... __args)
> > + : _M_args(std::forward<_Ts>(__args)...)
> > + { }
> >
> > // Invoke _Adaptor with arguments __r, _M_args... according to the
> > // value category of this _Partial object.
> > @@ -1046,10 +1051,12 @@ namespace views::__adaptor
> > {
> > _Arg _M_arg;
> >
> > - constexpr
> > - _Partial(_Arg __arg)
> > - : _M_arg(std::move(__arg))
> > - { }
> > + template<typename _Tp>
> > + requires (!same_as<remove_cvref_t<_Tp>, _Partial>)
> > + constexpr
> > + _Partial(_Tp&& __arg)
> > + : _M_arg(std::forward<_Tp>(__arg))
> > + { }
> >
> > template<typename _Range>
> > requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
> > @@ -1079,10 +1086,12 @@ namespace views::__adaptor
> > {
> > tuple<_Args...> _M_args;
> >
> > - constexpr
> > - _Partial(_Args... __args)
> > - : _M_args(std::move(__args)...)
> > - { }
> > + template<typename... _Ts>
> > + requires (sizeof...(_Ts) == sizeof...(_Args))
> > + constexpr
> > + _Partial(_Ts&&... __args)
> > + : _M_args(std::forward<_Ts>(__args)...)
> > + { }
> >
> > // Invoke _Adaptor with arguments __r, const _M_args&... regardless
> > // of the value category of this _Partial object.
> > @@ -1109,10 +1118,12 @@ namespace views::__adaptor
> > {
> > _Arg _M_arg;
> >
> > - constexpr
> > - _Partial(_Arg __arg)
> > - : _M_arg(std::move(__arg))
> > - { }
> > + template<typename _Tp>
> > + requires (!same_as<remove_cvref_t<_Tp>, _Partial>)
> > + constexpr
> > + _Partial(_Tp&& __arg)
> > + : _M_arg(std::forward<_Tp>(__arg))
> > + { }
> >
> > template<typename _Range>
> > requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
> > @@ -1135,10 +1146,11 @@ namespace views::__adaptor
> > [[no_unique_address]] _Lhs _M_lhs;
> > [[no_unique_address]] _Rhs _M_rhs;
> >
> > - constexpr
> > - _Pipe(_Lhs __lhs, _Rhs __rhs)
> > - : _M_lhs(std::move(__lhs)), _M_rhs(std::move(__rhs))
> > - { }
> > + template<typename _Tp, typename _Up>
> > + constexpr
> > + _Pipe(_Tp&& __lhs, _Up&& __rhs)
> > + : _M_lhs(std::forward<_Tp>(__lhs)),
> > _M_rhs(std::forward<_Up>(__rhs))
> > + { }
> >
> > // Invoke _M_rhs(_M_lhs(__r)) according to the value category of this
> > // range adaptor closure object.
> > @@ -1172,10 +1184,11 @@ namespace views::__adaptor
> > [[no_unique_address]] _Lhs _M_lhs;
> > [[no_unique_address]] _Rhs _M_rhs;
> >
> > - constexpr
> > - _Pipe(_Lhs __lhs, _Rhs __rhs)
> > - : _M_lhs(std::move(__lhs)), _M_rhs(std::move(__rhs))
> > - { }
> > + template<typename _Tp, typename _Up>
> > + constexpr
> > + _Pipe(_Tp&& __lhs, _Up&& __rhs)
> > + : _M_lhs(std::forward<_Tp>(__lhs)),
> > _M_rhs(std::forward<_Up>(__rhs))
> > + { }
> >
> > template<typename _Range>
> > requires __pipe_invocable<const _Lhs&, const _Rhs&, _Range>
> > --
> > 2.43.0.283.ga54a84b333
> >
>
>
