std::sized_sentinel_for, std::disable_sized_sentinel_for

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Iterator library
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(C++20)
sized_sentinel_for
(C++20)
(C++20)
(C++20)
(C++20)

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Common algorithm requirements
(C++20)
(C++20)
(C++20)
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(C++20)
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(C++11)(C++14)
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(C++17)
(C++17)
Defined in header <iterator>
template < class S, class I >

concept sized_sentinel_for =
std::sentinel_for <S, I> &&
!std:: disable_sized_sentinel_for < std::remove_cv_t <S>,
std::remove_cv_t <I>> &&
        requires( const I& i, const S& s) {
{ s - i } - > std::same_as < std::iter_difference_t <I>> ;
{ i - s } - > std::same_as < std::iter_difference_t <I>> ;

} ;
(1) (since C++20)
template < class S, class I >
inline constexpr bool disable_sized_sentinel_for = false ;
(2) (since C++20)
1) The sized_sentinel_for concept specifies that an object of the iterator type I and an object of the sentinel type S
2) The disable_sized_sentinel_for variable template can be used to prevent iterators and sentinels that can be subtracted but do not actually model sized_sentinel_for
A program may specialize disable_sized_sentinel_for for cv-unqualified non-array object type S and I, as long as at least one of which is a program-defined type. Such specializations are usable in constant expressions and have type const bool

Semantic requirements

Let i be an iterator of type I, and s a sentinel of type S such that [ i ,  s ) denotes a range. Let n be the smallest number of applications of ++i necessary to make bool(i == s) be true. I and S model sized_sentinel_for<S, I>

Equality preservation

Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving

Implicit expression variations

A requires expression that uses an expression that is non-modifying for some constant lvalue operand also requires implicit expression variations

See also

(C++20)
 specifies that a range knows its size in constant time
(concept)
(C++20)
 returns an integer equal to the size of a range
(customization point object)
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