std::ranges...w::iterator(3)

🦋 std::ranges...w::iterator(3) 🦋

okay so this is from the C++ Standard Libary manual, section (3). The title is exactly std::ranges...w::iterator(3) — yes, the dots are doing their thing — and we’re about to get into std::ranges::filter_view::iterator with full bestie energy. 💅

---

✨ NAME ✨

std::ranges::filter_view::iterator — literally std::ranges::filter_view::iterator. That’s the name, no cap.

🌈 Synopsis 🌈

class /*iterator*/;  (since C++20)
                     (exposition only*)

The return type of filter_view::begin. Slay.

This is a bidirectional_iterator if V models bidirectional_range, a forward_iterator if V models forward_range, and input_iterator otherwise.

🚨 Modification of the element denoted by this iterator is permitted, but results in undefined behavior if the resulting value does not satisfy the filter’s predicate. Like, you can do it, but if the predicate says no and you changed the value anyway, that’s UB, bestie. Be careful.

💖 Member types 💖

• iterator_concept — one of:
  • std::bidirectional_iterator_tag, if V models bidirectional_range,
  • std::forward_iterator_tag, if V models forward_iterator,
  • std::input_iterator_tag otherwise.
• iterator_category — defined if and only if V models forward_range. Let C be the type std::iterator_traits<ranges::iterator_t<V>>::iterator_category. Then:
  • std::bidirectional_iterator_tag, if C models std::derived_from<std::bidirectional_iterator_tag>,
  • std::forward_iterator_tag, if C models std::derived_from<std::forward_iterator_tag>,
  • C otherwise.
• value_type — ranges::range_value_t<V>.
• difference_type — ranges::range_difference_t<V>.

🌸 Data members 🌸

• current_ (private) — an iterator of type ranges::iterator_t<V> into the underlying view. (exposition-only member object*)
• parent_ (private) — a pointer of type ranges::filter_view<V, Pred>* to the parent filter_view object. (exposition-only member object*)

🎀 Member functions 🎀

• constructor (C++20) — constructs an iterator (public member function)
• base (C++20) — returns the underlying iterator (public member function)
• operator*, operator-> (C++20) — forwards to the underlying iterator (public member function)
• operator++, operator++(int) (C++20) — advances the iterator (public member function)
• operator--, operator--(int) (C++20) — decrements the iterator (public member function)

🔥 std::ranges::filter_view::iterator::iterator 🔥

/*iterator*/()
  requires std::default_initializable<ranges::iterator_t<V>> = default;

constexpr /*iterator*/( filter_view& parent,
                        ranges::iterator_t<V> current );

1. (since C++20) Initializes current_ and parent_ with their default member initializers, which are = ranges::iterator_t<V>() and = nullptr respectively.
2. (since C++20) Initializes current_ with std::move(current) and parent_ with std::addressof(parent).

🦋 std::ranges::filter_view::iterator::base 🦋

constexpr const ranges::iterator_t<V>& base() const & noexcept;
constexpr ranges::iterator_t<V> base() &&;

1. (since C++20) Equivalent to return current_;.
2. (since C++20) Equivalent to return std::move(current_);.

💜 std::ranges::filter_view::iterator::operator*,-> 💜

constexpr ranges::range_reference_t<V> operator*() const;
constexpr ranges::iterator_t<V> operator->() const
  requires /*has-arrow*/<ranges::iterator_t<V>> &&
           std::copyable<ranges::iterator_t<V>>;

1. (since C++20) Equivalent to return *current_;.
2. (since C++20) Equivalent to return current_;.

For a type I, /*has-arrow*/<I> is modeled or satisfied, if and only if I models or satisfies input_iterator respectively, and either I is a pointer type or requires(I i){ i.operator->();} is true.

⚡ std::ranges::filter_view::iterator::operator++ ⚡

constexpr /*iterator*/& operator++();
constexpr void operator++( int );
constexpr /*iterator*/ operator++( int )
  requires ranges::forward_range<V>;

1. (since C++20) Equivalent to

current_ = ranges::find_if(std::move(++current_),
                           ranges::end(parent_->base_),
                           std::ref(*parent_->pred_));

return *this;

2. (since C++20) Equivalent to ++*this;.
3. (since C++20) Equivalent to auto tmp = *this; ++*this; return tmp;.

🌙 std::ranges::filter_view::iterator::operator-- 🌙

constexpr /*iterator*/& operator--()
  requires ranges::bidirectional_range<V>;
constexpr /*iterator*/ operator--( int )
  requires ranges::bidirectional_range<V>;

1. (since C++20) Equivalent to

do

    --current_;
while (!std::invoke(*parent_->pred_, *current_));

return *this;

2. (since C++20) Equivalent to auto tmp = *this; --*this; return tmp;.

🌟 Non-member functions 🌟

• operator== (C++20) — compares the underlying iterators (function)
• iter_move (C++20) — casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function)
• iter_swap (C++20) — swaps the objects pointed to by two underlying iterators (function)

💅 operator==(std::ranges::filter_view::iterator) 💅

friend constexpr bool operator==( const /*iterator*/& x, const /*iterator*/& y )
  requires std::equality_comparable<ranges::iterator_t<V>>;

(since C++20) Equivalent to return x.current_ == y.current_;.

The != operator is synthesized from operator==.

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::ranges::filter_view::iterator is an associated class of the arguments.

🧚 iter_move(std::ranges::filter_view::iterator) 🧚

friend constexpr ranges::range_rvalue_reference_t<V>
  iter_move( const /*iterator*/& i )
    noexcept(noexcept(ranges::iter_move(i.current_)));

(since C++20) Equivalent to return ranges::iter_move(i.current_);.

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::ranges::filter_view::iterator is an associated class of the arguments.

🎀 iter_swap(std::ranges::filter_view::iterator) 🎀

friend constexpr void iter_swap( const /*iterator*/& x, const /*iterator*/& y )
  noexcept(noexcept(ranges::iter_swap(x.current_, y.current_)))
  requires std::indirectly_swappable<ranges::iterator_t<V>>;

(since C++20) Equivalent to ranges::iter_swap(x.current_, y.current_).

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::ranges::filter_view::iterator is an associated class of the arguments.

🩹 Defect reports 🩹

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• P2259R1 — applied to C++20; behavior as published: member type iterator_category was always defined; correct behavior: defined only if V is a forward_range.
• LWG 3533 — applied to C++20; behavior as published: the const& overload of base copied the underlying iterator; correct behavior: returns a reference to it.
• LWG 3593 — applied to C++20; behavior as published: the const& overload of base might not be noexcept; correct behavior: made noexcept.

---

💖 bestie, that’s the whole page. Source/version/date check: http://cppreference.com, 2024.06.10, and this is std::ranges...w::iterator(3). Bye, love you, go slay some ranges. 🫶