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

 

C++

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Standard Library Headers

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

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Regular expressions library (C++11)

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Technical Specifications

 

Ranges library

Range access
begincbegin endcend	rbegincrbegin rendcrend	size empty datacdata
Range primitives
iterator_tsentinel_t	range_difference_trange_value_t	range_reference_trange_rvalue_reference_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Semiregular wrapper
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	views::counted
Adaptors
all_viewviews::all join_viewviews::join take_viewviews::take basic_istream_viewistream_view	ref_view                                split_viewviews::split take_while_viewviews::take_while elements_viewviews::elements	common_viewviews::common transform_viewviews::transform drop_viewviews::drop keys_viewviews::keys	reverse_viewviews::reverse filter_viewviews::filter drop_while_viewviews::drop_while values_viewviews::values

 

Defined in header <ranges>
template< class T > concept sized_range = ranges::range<T> &&   ! ranges::disable_sized_range<std::remove_cvref_t<T>> &&   requires(T& t) {     ranges::size(t);   };	(1)
template<class> inline constexpr bool disable_sized_range = false;	(2)

1) The sized_range concept specifies the requirements of a range type that knows its size in constant time with the size function.

Formally, given an lvalue t of type std::remove_reference_t<T>, T models sized_range only if

• ranges::size(t)

• has non-amortized constant-time complexity,
• does not modify t, and
• is equal to ranges::distance(t), and

• if 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)

2) disable_sized_range exists to allows use of range types that satisfy but do not in fact model sized_range.

Notes

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.