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operator==,<,>,<=,>=,<=>(ranges::concat_view::iterator)

From cppreference.com
 
 
Ranges library
Range adaptors
 
 
friend constexpr bool operator== ( const /*iterator*/& x, std::default_sentinel_t );
(1) (since C++26)
friend constexpr bool operator== ( const /*iterator*/& x, const /*iterator*/& y ) requires (std::equality_comparable<ranges::iterator_t< std::conditional_t<Const, const Views, Views>>> && ...);
(2) (since C++26)
friend constexpr bool operator< ( const /*iterator*/& x, const /*iterator*/& y ) requires /*all-random-access*/<Const, Views...>;
(3) (since C++26)
friend constexpr bool operator> ( const /*iterator*/& x, const /*iterator*/& y ) requires /*all-random-access*/<Const, Views...>;
(4) (since C++26)
friend constexpr bool operator<= ( const /*iterator*/& x, const /*iterator*/& y ) requires /*all-random-access*/<Const, Views...>;
(5) (since C++26)
friend constexpr bool operator>= ( const /*iterator*/& x, const /*iterator*/& y ) requires /*all-random-access*/<Const, Views...>;
(6) (since C++26)
friend constexpr auto operator<=> ( const /*iterator*/& x, const /*iterator*/& y ) requires (/*all-random-access*/<Const, Views...> && (std::three_way_comparable<ranges::iterator_t< std::conditional_t<Const, const Views, Views>>> && ...));
(7) (since C++26)

Compares the iterator with another iterator or a sentinel.

1) Compares an iterator with a sentinel.
If x.it_ .valueless_by_exception() is true, the behavior is undefined.
2-7) Compares two iterators. The != operator is synthesized from operator==.
If x.it_ .valueless_by_exception() || y.it_ .valueless_by_exception() is true, the behavior is undefined.

These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::ranges::concat_view::iterator <Const> is an associated class of the arguments.

Parameters

x, y - iterators to compare

Return value

1)

x.it_ .index() == (sizeof...(Views) - 1) &&
    x.get-iter <sizeof...(Views) - 1>() == x.get-end <sizeof...(Views) - 1>()

2) x.it_ == y.it_
3) x.it_ < y.it_
4) x.it_ > y.it_
5) x.it_ <= y.it_
6) x.it_ >= y.it_
7) x.it_ <=> y.it_

Example