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std::ranges::filter_view<V,Pred>::iterator 

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

The return type of filter_view::begin. The name iterator is for exposition purposes only.

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.

Member types

Member type Definition
iterator_concept
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.
value_type ranges::range_value_t<V>
difference_type ranges::range_difference_t<V>

Data members

Typical implementations of iterator hold two non-static data members:

  • an iterator of type ranges::iterator_t<V> into the underlying view (shown here as current_ for exposition only), and
  • a pointer of type ranges::filter_view<V, Pred>* to the parent filter_view object (shown here as parent_ for exposition only).

Member functions

(C++20)
 constructs an iterator
(public member function)
(C++20)
 returns the underlying iterator
(public member function)
(C++20)
 forwards to the underlying iterator
(public member function)
(C++20)
 advances the iterator
(public member function)
(C++20)
 decrements the iterator
(public member function)

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

/*iterator*/()
  requires std::default_initializable<ranges::iterator_t<V>> = default;
 (1) (since C++20) 
constexpr /*iterator*/( filter_view& parent,
                        ranges::iterator_t<V> current );
 (2) (since C++20)
1) Initializes current_ and parent_ with their default member initializers, which are = ranges::iterator_t<V>() and = nullptr respectively.
2) 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;
 (1) (since C++20) 
constexpr ranges::iterator_t<V> base() &&;
 (2) (since C++20)
1) Equivalent to return current_;.
2) Equivalent to return std::move(current_);.

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

constexpr ranges::range_reference_t<V> operator*() const;
 (1) (since C++20) 
constexpr ranges::iterator_t<V> operator->() const
  requires /*has-arrow*/<ranges::iterator_t<V>> &&
           std::copyable<ranges::iterator_t<V>>;
 (2) (since C++20)
1) Equivalent to return *current_;.
2) 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++();
 (1) (since C++20) 
constexpr void operator++( int );
 (2) (since C++20) 
constexpr /*iterator*/ operator++( int )
  requires ranges::forward_range<V>;
 (3) (since C++20)
1) Equivalent to
current_ = ranges::find_if(std::move(++current_), ranges::end(parent_->base_),

std::ref(*parent_->pred_));

return *this;.
2) Equivalent to ++*this;.
3) Equivalent to auto tmp = *this; ++*this; return tmp;.

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

constexpr /*iterator*/& operator--()
  requires ranges::bidirectional_range<V>;
 (1) (since C++20) 
constexpr /*iterator*/ operator--( int )
  requires ranges::bidirectional_range<V>;
 (2) (since C++20)
1) Equivalent to
do

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

return *this;.
2) Equivalent to auto tmp = *this; --*this; return tmp;.

Non-member functions

(C++20)
 compares the underlying iterators
(function)
(C++20)
 casts the result of dereferencing the underlying iterator to its associated rvalue reference type
(function)
(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.

DR Applied to Behavior as published Correct behavior
P2259R1 C++20 member type iterator_category was always defined defined only if V is a forward_range
LWG 3533 C++20 the const& overload of base copied the underlying iterator returns a reference to it
LWG 3593 C++20 the const& overload of base might not be noexcept made noexcept

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