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

< cpp‎ | ranges
Defined in header <ranges>
template< class T >

concept sized_range = ranges::range<T> &&
  requires(T& t) {

(1) (since C++20)
inline constexpr bool disable_sized_range = false;
(2) (since C++20)
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.

[edit] Semantic requirements

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

[edit] 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.