std::ranges::borrowed_range, std::ranges::enable_borrowed_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)

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Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_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
views::all_tviews::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 R> concept borrowed_range =     ranges::range<R> &&     (std::is_lvalue_reference_v<R> || ranges::enable_borrowed_range<std::remove_cvref_t<R>>);	(1)
Defined in header <ranges>
Defined in header <span>
Defined in header <string_view>
template<class R> inline constexpr bool enable_borrowed_range = false;	(2)

1) The concept borrowed_range defines the requirements of a range such that a function can take it by value and return iterators obtained from it without danger of dangling.

2) The enable_borrowed_range variable template is used to indicate whether a range is a borrowed_range. The primary template is defined as false.
Specializations for all specializations of the following standard templates are defined as true:

• std::basic_string_view
• std::span
• std::ranges::subrange
• std::ranges::ref_view
• std::ranges::empty_view
• std::ranges::iota_view

enable_borrowed_range is permitted to be specialized for cv-unqualified program-defined types.

Semantic requirements

Given an expression e such that decltype((e)) is T, T models borrowed_range only if the validity of iterators obtained from the object denoted by e is not tied to the lifetime of that object.

Notes

Users may specialize enable_borrowed_range to true for cv-unqualified program-defined types which model borrowed_range, and false for types which do not. Such specializations shall be usable in constant expressions and have type const bool.