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?
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
>
