Re: [PATCH] libstdc++/ranges: Define _S_has_simple_call_op on newer adaptors

[Patrick Palka <ppalka@redhat.com>]

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On Wed, 17 Jan 2024, Jonathan Wakely wrote:

> 
> 
> On Wed, 17 Jan 2024, 02:37 Patrick Palka, <ppalka@redhat.com> wrote:
>       Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> 
> 
> OK

Thanks a lot.  For the record I ended up not pushing this patch because
all the range adaptors it touches are C++23 ones and so ...

> 
> 
> 
>       -- >8 --
> 
>       This compile-time and diagnostic improvement[1] is less important in
>       C++23 mode where deducing this is available and used in _Pipe, but for
>       benefit of C++20 mode

... this isn't true.  There's no real benefit in setting this flag for
standard C++23 range adaptors (besides consistency I guess, but OTOH not
setting it means more testing coverage for the deducing this code path).

> and for consistency let's set the flag on the most
>       recently added range adaptors which lack it.
> 
>       [1]: Defining _S_has_simple_call_op=true for a range adaptor closure
>       object signals that the adaptor has an operator() that's not overloaded
>       according to the constness/value category of the object, which in turn
>       allows us to implement the operator() of the composition of such adaptors
>       in a simpler way.
> 
>       libstdc++-v3/ChangeLog:
> 
>               * include/std/ranges (views::_Adjacent::_S_has_simple_call_op):
>               Define to true.
>               (views::_AsRvalue::_S_has_simple_call_op): Likewise.
>               (views::_Enumerate::_S_has_simple_call_op): Likewise.
>               (views::_AsConst::_S_has_simple_call_op): Likewise.
>       ---
>        libstdc++-v3/include/std/ranges | 8 ++++++++
>        1 file changed, 8 insertions(+)
> 
>       diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
>       index 7ef835f486a..66502cc1da4 100644
>       --- a/libstdc++-v3/include/std/ranges
>       +++ b/libstdc++-v3/include/std/ranges
>       @@ -5669,6 +5669,8 @@ namespace views::__adaptor
>                   else
>                     return adjacent_view<all_t<_Range>, _Nm>(std::forward<_Range>(__r));
>                 }
>       +
>       +       static constexpr bool _S_has_simple_call_op = true;
>              };
> 
>            template<size_t _Nm>
>       @@ -8844,6 +8846,8 @@ namespace views::__adaptor
>                 else
>                   return as_rvalue_view(std::forward<_Range>(__r));
>               }
>       +
>       +      static constexpr bool _S_has_simple_call_op = true;
>            };
> 
>            inline constexpr _AsRvalue as_rvalue;
>       @@ -9147,6 +9151,8 @@ namespace views::__adaptor
>               constexpr auto
>               operator() [[nodiscard]] (_Range&& __r) const
>               { return enumerate_view<all_t<_Range>>(std::forward<_Range>(__r)); }
>       +
>       +      static constexpr bool _S_has_simple_call_op = true;
>            };
> 
>            inline constexpr _Enumerate enumerate;
>       @@ -9253,6 +9259,8 @@ namespace views::__adaptor
>               else
>                 return as_const_view(std::forward<_Range>(__r));
>              }
>       +
>       +      static constexpr bool _S_has_simple_call_op = true;
>            };
> 
>            inline constexpr _AsConst as_const;
>       --
>       2.43.0.367.g186b115d30
> 
> 
>