std::ranges::sized_range, std::ranges::disable_sized_range
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Ranges library
(until C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++26)(C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
Defined in header
<ranges>
(1)
template< class T >
(since C++20) concept sized_range = ranges::range <T> &&
requires(T& t) {
ranges::size (t);
(until C++26)
template< class T >
(since C++26)
concept sized_range = ranges::approximately_sized_range<T> &&
requires(T& t) {
ranges::size (t);
template< class >
constexpr bool disable_sized_range = false;
(2)
(since C++20)
constexpr bool disable_sized_range = false;
1) The
sized_range concept specifies the requirements of a range (until C++26)approximately_sized_range (since C++26) 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.[edit] 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).
[edit] 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.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_reserve_hint |
202502L |
(C++26) | ranges::approximately_sized_range and ranges::reserve_hint |
[edit] 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() {}