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From: "rs2740 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/100631] ranges::elements_view:: _Sentinel is missing
 __distance_from() that can access _M_current of _Iterator
Date: Mon, 17 May 2021 12:32:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100631

TC <rs2740 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rs2740 at gmail dot com

--- Comment #4 from TC <rs2740 at gmail dot com> ---
(In reply to =E5=BA=B7=E6=A1=93=E7=91=8B from comment #1)
> Another issue is that in elements_view::_Sentinel in ranges#L3677:
>=20
>=20
>   template<bool _Const2,
>            typename _Base2 =3D __detail::__maybe_const_t<_Const2, _Vp>>
>     requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
>     friend constexpr range_difference_t<_Base2>
>     operator-(const _Iterator<_Const2>& __x, const _Sentinel& __y)
>     { return __x._M_current - __y._M_end; }
>=20
>=20
> the return type of the function is range_difference_t<_Base2>, but in
> [range.elements#sentinel], it is defined as range_difference_t<Base>:
>=20
>=20
>   template<bool OtherConst>
>     requires sized_=C2=ADsentinel_=C2=ADfor<sentinel_t<Base>, iterator_t<=
maybe-=20
>   const<OtherConst, V>>>
>   friend constexpr range_difference_t<Base>
>     operator-(const iterator<OtherConst>& x, const sentinel& y);
>=20
>=20
> Perhaps range_difference_t<Base> and range_difference_t<_Base2> are
> equivalent in this case, but I am not sure.

This one is a problem with the WP.=