[PATCH 3/4] libstdc++: Implement ranges::chunk_view from P2442R1

[Jonathan Wakely]

On Mon, 12 Sept 2022 at 17:48, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> This also implements the LWG 3707, 3710 and 3712 changes to chunk_view.


> +
> +  template<view _Vp>
> +    requires input_range<_Vp>
> +  class chunk_view<_Vp>::_OuterIter
> +  {
> +    chunk_view* _M_parent;
> +
> +    constexpr explicit
> +    _OuterIter(chunk_view& __parent)

This can be noexcept.

> +      : _M_parent(std::__addressof(__parent))
> +    { }
> +
> +    friend chunk_view;
> +
> +  public:
> +    using iterator_concept = input_iterator_tag;
> +    using difference_type = range_difference_t<_Vp>;
> +
> +    struct value_type;
> +
> +    _OuterIter(_OuterIter&&) = default;
> +    _OuterIter& operator=(_OuterIter&&) = default;
> +
> +    constexpr value_type
> +    operator*() const
> +    {
> +      __glibcxx_assert(*this != default_sentinel);
> +      return value_type(*_M_parent);
> +    }
> +
> +    constexpr _OuterIter&
> +    operator++()
> +    {
> +      __glibcxx_assert(*this != default_sentinel);
> +      ranges::advance(*_M_parent->_M_current, _M_parent->_M_remainder,
> +                     ranges::end(_M_parent->_M_base));
> +      _M_parent->_M_remainder = _M_parent->_M_n;
> +      return *this;
> +    }
> +
> +    constexpr void
> +    operator++(int)
> +    { ++*this; }
> +
> +    friend constexpr bool
> +    operator==(const _OuterIter& __x, default_sentinel_t)
> +    {
> +      return *__x._M_parent->_M_current == ranges::end(__x._M_parent->_M_base)
> +       && __x._M_parent->_M_remainder != 0;
> +    }
> +
> +    friend constexpr difference_type
> +    operator-(default_sentinel_t, const _OuterIter& __x)
> +    requires sized_sentinel_for<sentinel_t<_Vp>, iterator_t<_Vp>>
> +    {
> +      const auto __dist = ranges::end(__x._M_parent->_M_base) - *__x._M_parent->_M_current;
> +
> +      if (__dist < __x._M_parent->_M_remainder)
> +       return __dist == 0 ? 0 : 1;
> +
> +      return 1 + __detail::__div_ceil(__dist - __x._M_parent->_M_remainder,
> +                                     __x._M_parent->_M_n);
> +    }
> +
> +    friend constexpr difference_type
> +    operator-(const _OuterIter& __x, default_sentinel_t __y)
> +    requires sized_sentinel_for<sentinel_t<_Vp>, iterator_t<_Vp>>
> +    { return -(__y - __x); }
> +  };
> +
> +  template<view _Vp>
> +    requires input_range<_Vp>
> +  struct chunk_view<_Vp>::_OuterIter::value_type : view_interface<value_type>
> +  {
> +  private:
> +    chunk_view* _M_parent;
> +
> +    constexpr explicit
> +    value_type(chunk_view& __parent)

And this.

> +    : _M_parent(std::__addressof(__parent))
> +    { }
> +
> +    friend _OuterIter;
> +



> +  template<view _Vp>
> +    requires input_range<_Vp>
> +  class chunk_view<_Vp>::_InnerIter
> +  {
> +    chunk_view* _M_parent;
> +
> +    constexpr explicit
> +    _InnerIter(chunk_view& __parent) noexcept

And this already is, so that's nice.


> +    : _M_parent(std::__addressof(__parent))
> +    { }
> +
> +    friend _OuterIter::value_type;
> +
> +  public:
> +    using iterator_concept = input_iterator_tag;
> +    using difference_type = range_difference_t<_Vp>;
> +    using value_type = range_value_t<_Vp>;
> +
> +    _InnerIter(_InnerIter&&) = default;
> +    _InnerIter& operator=(_InnerIter&&) = default;
> +
> +    constexpr const iterator_t<_Vp>&
> +    base() const &
> +    { return *_M_parent->_M_current; }
> +
> +    constexpr range_reference_t<_Vp>
> +    operator*() const
> +    {
> +      __glibcxx_assert(*this != default_sentinel);
> +      return **_M_parent->_M_current;
> +    }
> +
> +    constexpr _InnerIter&
> +    operator++()
> +    {
> +      __glibcxx_assert(*this != default_sentinel);
> +      ++*_M_parent->_M_current;
> +      if (*_M_parent->_M_current == ranges::end(_M_parent->_M_base))
> +       _M_parent->_M_remainder = 0;
> +      else
> +       --_M_parent->_M_remainder;
> +      return *this;
> +    }
> +
> +    constexpr void
> +    operator++(int)
> +    { ++*this; }
> +
> +    friend constexpr bool
> +    operator==(const _InnerIter& __x, default_sentinel_t)

noexcept

OK with those tweaks.