std::ranges::SizedRange, std::ranges::disable_sized_range

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

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

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

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Technical Specifications

 

Ranges library

Range access
begincbegin endcend	rbegincrbegin rendcrend	size empty datacdata
Range primitives
iterator_t	sentinel_t
Dangling iterator handling
dangling	safe_iterator_t	safe_subrange_t
Range concepts
Range SizedRange View	InputRange OutputRange ForwardRange	BidirectionalRange RandomAccessRange ContiguousRange	CommonRange ViewableRange
Views
view_interface	subrange
Semiregular wrapper
Factories
empty_viewview::empty	single_viewview::single	iota_viewview::iota	view::counted
Adaptors
all_viewview::all ref_view filter_viewview::filter	transform_viewview::transform                                take_viewview::take	join_viewview::join split_viewview::split	common_viewview::common reverse_viewview::reverse

 

Defined in header <ranges>
template< class T > concept SizedRange = Range<T> &&   ! 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 SizedRange 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 SizedRange 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 ForwardIterator, 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 SizedRange.