Re: [PATCH] libstdc++: Make __max_size_type and __max_diff_type structural

[Patrick Palka <ppalka@redhat.com>]

On Mon, Apr 24, 2023 at 12:23 PM Patrick Palka <ppalka@redhat.com> wrote:
>
> This patch makes these integer-class type structural types by changing
> their private data members into public ones, which allows them to be
> used as NTTP types.  I'm not sure if this is required by the standard
> but it seems handy.
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

Ping

>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/max_size_type.h (__max_size_type::_M_val): Make
>         public instead of private.
>         (__max_size_type::_M_msb): Likewise.
>         (__max_diff_type::_M_rep): Likewise.
>         * testsuite/std/ranges/iota/max_size_type.cc: Verify
>         __max_diff_type and __max_size_type are structural.
> ---
>  libstdc++-v3/include/bits/max_size_type.h               | 4 ++--
>  libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc | 7 +++++++
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/max_size_type.h b/libstdc++-v3/include/bits/max_size_type.h
> index 4796135d073..d6705bbe4c8 100644
> --- a/libstdc++-v3/include/bits/max_size_type.h
> +++ b/libstdc++-v3/include/bits/max_size_type.h
> @@ -423,10 +423,11 @@ namespace ranges
>        using __rep = unsigned long long;
>  #endif
>        static constexpr size_t _S_rep_bits = sizeof(__rep) * __CHAR_BIT__;
> -    private:
> +
>        __rep _M_val = 0;
>        unsigned _M_msb:1 = 0;
>
> +    private:
>        constexpr explicit
>        __max_size_type(__rep __val, int __msb) noexcept
>         : _M_val(__val), _M_msb(__msb)
> @@ -750,7 +751,6 @@ namespace ranges
>        { return !(__l < __r); }
>  #endif
>
> -    private:
>        __max_size_type _M_rep = 0;
>
>        friend class __max_size_type;
> diff --git a/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc b/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> index 985acd5a803..9afd05d5acf 100644
> --- a/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/iota/max_size_type.cc
> @@ -400,6 +400,13 @@ static_assert(max_diff_t(max_size_t(1)
>                          << (numeric_limits<max_size_t>::digits-1))
>               == numeric_limits<max_diff_t>::min());
>
> +// Verify that the types are structural types and can therefore be used
> +// as NTTP types.
> +template<max_size_t V> struct Su { static_assert(V*V == V+132); };
> +template<max_diff_t V> struct Ss { static_assert(V*V == V+132); };
> +template struct Su<12>;
> +template struct Ss<12>;
> +
>  int
>  main()
>  {
> --
> 2.40.0.374.g7580f92ffa
>