std::ranges::sized_range, std::ranges::disable_sized_range
From cppreference.com
| Defined in header <ranges>
|
||
| template< class T > concept sized_range = ranges::range<T> && |
(1) | (since C++20) |
| template< class > 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) The
disable_sized_range exists to allow 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
tin 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
Run this code
#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
| (C++20) |
specifies a range whose iterator type satisfies random_access_iterator (concept) |
| (C++20) |
specifies a range whose iterator type satisfies contiguous_iterator (concept) |