NAME

std::ranges::sized_range,std::ranges::disable_sized_range - std::ranges::sized_range,std::ranges::disable_sized_range

Synopsis

Defined in header <ranges>
template< class T >

concept sized_range = ranges::range<T> &&
requires(T& t) { (1) (since C++20)
ranges::size(t);

};
template< class > (2) (since C++20)
inline constexpr bool disable_sized_range = false;

1) The sized_range concept specifies the requirements of a range type that knows its
size in constant time with the size function.
2) disable_sized_range exists to allows use of range types that provide a size
function (either as a member or as a non-member) but do not in fact model
sized_range. Users may specialize disable_sized_range for cv-unqualified
program-defined types. Such specializations shall be usable in constant expressions
and have type const bool.

Semantic requirements

1) Given an lvalue t of type std::remove_reference_t<T>, T models sized_range only
if

* ranges::size(t)

* has amortized constant-time complexity,
* does not alter the value of t in a manner observable to
equality-preserving expressions, and
* is equal to ranges::distance(ranges::begin(t), ranges::end(t)), and

* if ranges::iterator_t<T> models forward_iterator, ranges::size(t) is
well-defined regardless of the evaluation of ranges::begin(t) (in other words, a
single-pass sized range may support a call to size only before the first call to
begin, but a forward range must support size at all times).

Notes

disable_sized_range cannot be used to opt-out a range whose iterator and sentinel
satisfy sized_sentinel_for; disable_sized_sentinel_for must be used instead.

disable_sized_range cannot be specialized for array types or reference types.

Example

// Run this code

#include <ranges>
#include <list>
#include <forward_list>

int main()
{
static_assert(std::ranges::sized_range<std::list<int>>
and not std::ranges::sized_range<std::forward_list<int>>);
}

See also

ranges::random_access_range specifies a range whose iterator type satisfies
(C++20) random_access_iterator
(concept)
ranges::contiguous_range specifies a range whose iterator type satisfies
(C++20) contiguous_iterator
(concept)