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From: "hewillk at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/100631] ranges::elements_view:: _Sentinel is missing
 __distance_from() that can access _M_current of _Iterator
Date: Mon, 17 May 2021 03:45:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100631

--- Comment #1 from =E5=BA=B7=E6=A1=93=E7=91=8B <hewillk at gmail dot com> =
---
Another issue is that in elements_view::_Sentinel in ranges#L3677:


  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; }


the return type of the function is range_difference_t<_Base2>, but in
[range.elements#sentinel], it is defined as range_difference_t<Base>:


  template<bool OtherConst>
    requires sized_=C2=ADsentinel_=C2=ADfor<sentinel_t<Base>, iterator_t<ma=
ybe-=20
  const<OtherConst, V>>>
  friend constexpr range_difference_t<Base>
    operator-(const iterator<OtherConst>& x, const sentinel& y);


Perhaps range_difference_t<Base> and range_difference_t<_Base2> are equival=
ent
in this case, but I am not sure.=