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

From cppreference.com
< cpp‎ | ranges
 
 
Ranges library
 
Defined in header <ranges>
(1)
template< class T >

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

    };
(since C++20)
(until C++26)
template< class T >

concept sized_range = ranges::approximately_sized_range<T> &&
    requires(T& t) {
        ranges::size (t);

    };
(since C++26)
template< class >
constexpr bool disable_sized_range = false;
(2) (since C++20)
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

[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() {}

[edit] See also

specifies a range whose iterator type satisfies random_access_iterator
(concept) [edit]
specifies a range whose iterator type satisfies contiguous_iterator
(concept) [edit]

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