std::ranges::concat_view<Views...>::iterator

template< bool Const > class /iterator/	(1)	(exposition only*)
Helper concepts
template< bool Const, class... Rs > concept /concat-is-random-access/ = /* see description */;	(2)	(exposition only*)
template< bool Const, class... Rs > concept /concat-is-bidirectional/ = /* see description */;	(3)	(exposition only*)

1) ranges::concat_view<Views...>::iterator is the type of the iterators returned by begin() and end() of ranges::concat_view<Views...>.

2) Let Fs be the pack that consists of all elements of Rs except the last element. Equivalent to

 template<boolConst,class...Rs>
 concept concat-is-random-access =// exposition only
     all-random-access <Const,Rs...>&&
     (ranges::common_range<maybe-const <Const,Fs>>&&...);

3) Let Fs be the pack that consists of all elements of Rs except the last element. Equivalent to

 template<boolConst,class...Rs>
 concept concat-is-bidirectional =// exposition only
     all-bidirectional <Const,Rs...>&&
     (ranges::common_range<maybe-const <Const,Fs>>&&...);

Template parameters

Const

whether the iterator is a constant iterator

Nested types

Type	Definition
Exposition-only types
`base-iter`	std::variant<ranges::iterator_t<`maybe-const` <Const,Views>>...> (exposition-only member type*)
Iterator property types
Type	Definition
`iterator_concept`	an iterator tag, see below
`iterator_category` (conditionally present)	an iterator tag, see below
`value_type`	`concat-value-t` <`maybe-const` <Const,Views>...>
`difference_type`	std::common_type_t<ranges::range_difference_t<`maybe-const` <Const,Views>>...>

Determining the iterator concept

iterator_concept is defined as follows:

If concat-is-random-access <Const,Views...> is modeled, iterator_concept denotes std::random_access_iterator_tag.
Otherwise, if concat-is-bidirectional <Const,Views...> is modeled, iterator_concept denotes std::bidirectional_iterator_tag.
Otherwise, if all-forward <Const,Views...> is modeled, iterator_concept denotes std::forward_iterator_tag.
Otherwise, iterator_concept denotes std::input_iterator_tag.

Determining the iterator category

iterator_category is defined if and only if all-forward <Const,Views...> is modeled. In this case, it is defined as follows:

If std::is_reference_v<concat-reference-t <maybe-const <Const,Views>...>> is false, iterator_category denotes std::input_iterator_tag.
Otherwise, let Cs denote the pack of types std::iterator_traits<ranges::iterator_t<maybe-const <Const,Views>>>::iterator_category...:
- If (std::derived_from<Cs,std::random_access_iterator_tag>&&...)&& concat-is-random-access <Const,Views...> is true, iterator_category denotes std::random_access_iterator_tag.
- Otherwise, if (std::derived_from<Cs,std::bidirectional_iterator_tag>&&...)&& concat-is-bidirectional <Const,Views...> is true, iterator_category denotes std::bidirectional_iterator_tag.
- Otherwise, if (std::derived_from<Cs, std::forward_iterator_tag> && ...) is true, iterator_category denotes std::forward_iterator_tag.
- Otherwise, iterator_category denotes std::input_iterator_tag.

Data members

Member	Description
`maybe-const` <Const,ranges::concat_view>* `parent_`	a pointer to the parent `concat_view` (exposition-only member object*)
`base-iter` `it_`	an iterator into the current view (exposition-only member object*)

Member functions

(constructor)	constructs an iterator (public member function)
operator*	accesses the element (public member function)
operator[]	accesses an element by index (public member function)
operator++operator++(int)operator--operator--(int)operator+=operator-=	advances or decrements the underlying iterator (public member function)
Exposition-only function templates
satisfy	replaces `it_` with the beginning of the next view, if `it_` is the end of current view (exposition-only member function*)
prev	decrements `it_` such that it points to the previous position (exposition-only member function*)
advance-fwd	advances the current position on given offset (exposition-only member function*)
advance-bwd	decrements the current position on given value (exposition-only member function*)

Non-member functions

operator==operator<operator>operator<=operator>=operator<=> (C++26)	compares the underlying iterators (function)
operator+operator- (C++26)	performs iterator arithmetic (function)
iter_move (C++26)	casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function)
iter_swap (C++26)	swaps the objects pointed to by two underlying iterators (function)

Example

The preliminary version can be checked out on Compiler Explorer.

#include <iostream>
#include <iterator>
#include <ranges>

int main()
{
    namespace views = std::views;
    static constexpr int p[]{1, 2, 3};
    static constexpr auto e = {4, 5};
    auto t = views::iota(6, 9);
    auto cat = views::concat(p, e, t);
    auto dog = views::concat(cat, cat);
    for (auto i{dog.begin()}; i != std::default_sentinel; ++i)
        std::cout << *i << ' ';
    std::cout << '\n';
}

Output:

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

References

C++26 standard (ISO/IEC 14882:2026):

26.7.18.3 Class template concat_view::iterator [range.concat.iterator]

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