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

 

C++

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Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
range_size_trange_difference_trange_value_trange_reference_t	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)	elements_of (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Range factories
empty_viewviews::empty single_viewviews::single	iota_viewviews::iota repeat_viewviews::repeat (C++23)(C++23)	basic_istream_viewviews::istream
Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23) filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23) lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)
Range generators
std::generator (C++23)
Range adaptor objects
Range adaptor closure objects
range_adaptor_closure (C++23)
Helper items
copyable-box movable-box (until C++23)(C++23)	simple-view non-propagating-cache

 

Defined in header <ranges>
template< class T > concept sized_range = ranges::range<T> &&   requires(T& t) {     ranges::size(t);   };	(1)	(since C++20)
template< class > 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 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 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).

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

ranges::random_access_range (C++20)	specifies a range whose iterator type satisfies random_access_iterator (concept)
ranges::contiguous_range (C++20)	specifies a range whose iterator type satisfies contiguous_iterator (concept)