Re: [PATCH v3 1/3] c++, libstdc++: Implement __is_arithmetic built-in trait

[Jonathan Wakely <jwakely@redhat.com>]

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On Sat, 22 Jul 2023 at 14:51, François Dumont via Libstdc++ <
libstdc++@gcc.gnu.org> wrote:

>
> On 18/07/2023 08:27, Ken Matsui via Libstdc++ wrote:
> > This patch implements built-in trait for std::is_arithmetic.
> >
> > gcc/cp/ChangeLog:
> >
> >       * cp-trait.def: Define __is_arithmetic.
> >       * constraint.cc (diagnose_trait_expr): Handle CPTK_IS_ARITHMETIC.
> >       * semantics.cc (trait_expr_value): Likewise.
> >       (finish_trait_expr): Likewise.
> >
> > gcc/testsuite/ChangeLog:
> >
> >       * g++.dg/ext/has-builtin-1.C: Test existence of __is_arithmetic.
> >       * g++.dg/ext/is_arithmetic.C: New test.
> >       * g++.dg/tm/pr46567.C (__is_arithmetic): Rename to ...
> >       (__is_arith): ... this.
> >       * g++.dg/torture/pr57107.C: Likewise.
> >
> > libstdc++-v3/ChangeLog:
> >
> >       * include/bits/cpp_type_traits.h (__is_arithmetic): Rename to ...
> >       (__is_arith): ... this.
> >       * include/c_global/cmath: Use __is_arith instead.
> >       * include/c_std/cmath: Likewise.
> >       * include/tr1/cmath: Likewise.
> >
> > Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
> > ---
> >   gcc/cp/constraint.cc                        |  3 ++
> >   gcc/cp/cp-trait.def                         |  1 +
> >   gcc/cp/semantics.cc                         |  4 ++
> >   gcc/testsuite/g++.dg/ext/has-builtin-1.C    |  3 ++
> >   gcc/testsuite/g++.dg/ext/is_arithmetic.C    | 33 ++++++++++++++
> >   gcc/testsuite/g++.dg/tm/pr46567.C           |  6 +--
> >   gcc/testsuite/g++.dg/torture/pr57107.C      |  4 +-
> >   libstdc++-v3/include/bits/cpp_type_traits.h |  4 +-
> >   libstdc++-v3/include/c_global/cmath         | 48 ++++++++++-----------
> >   libstdc++-v3/include/c_std/cmath            | 24 +++++------
> >   libstdc++-v3/include/tr1/cmath              | 24 +++++------
> >   11 files changed, 99 insertions(+), 55 deletions(-)
> >   create mode 100644 gcc/testsuite/g++.dg/ext/is_arithmetic.C
>
>

[...]


> diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h
> b/libstdc++-v3/include/bits/cpp_type_traits.h
> > index 4312f32a4e0..d00d1ea8d75 100644
> > --- a/libstdc++-v3/include/bits/cpp_type_traits.h
> > +++ b/libstdc++-v3/include/bits/cpp_type_traits.h
> > @@ -381,7 +381,7 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
> >     // An arithmetic type is an integer type or a floating point type
> >     //
> >     template<typename _Tp>
> > -    struct __is_arithmetic
> > +    struct __is_arith
> >       : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> >
> >       { };
>
> 'ptr' is a well known alias of 'pointer', I wouldn't say the same for
> 'arith' and 'arithmetic'.
>
> But wait for a native-english feedback to change anything.
>
>

I think it's clear enough. This is only an internal trait anyway, not part
of a public API.

Since all uses are with the __enable_if trait, we could add this helper and
get rid of __is_arithmetic completely:

template<typename _Tp, typename _Res,
                bool = __is_integer<_Tp>::__value ||
__is_floating<_Tp>::__value>
struct __enable_if_arithmetic { };

template<typename _Tp, typename _Res>
struct __enable_if_arithmetic<_Tp, _Res, true> { typedef _Res __type; };

And similarly for a two-argument __enable_if_both_arithmetic helper.

But we can consider doing that later, I think __is_arith is fine for now.

The libstdc++ parts of this patch are OK (but wait for approval for the
compiler changes from a G++ maintainer before pushing).