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

template< class T >
concept sized_range = ranges::range<T> &&
    requires(T& t) {
        ranges::size(t);
    };

template< class >
inline constexpr bool disable_sized_range = false;

Semantic requirements

• 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; std::disable_sized_sentinel_for must be used instead.

disable_sized_range cannot be specialized for array types or reference types.

Example

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

See also