std::ranges::sized_range, std::ranges::disable_sized_range
From cppreference.com
Defined in header <ranges>
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||
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template
<
class T >
concept sized_range =
ranges::range
<T>
&&
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(1) | (since C++20) |
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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
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) )
- if ranges::iterator_t<T> models
forward_iterator, ranges::size(t) is well-defined regardless of the evaluation of ranges::begin(t)
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
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
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(C++20)
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specifies a range whose iterator type satisfies random_access_iterator (concept) |
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(C++20)
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specifies a range whose iterator type satisfies contiguous_iterator (concept) |