std::ranges::borrowed_range,std::ranges::enable_borrowed_range

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Ranges library

Range access

begin
cbegin
end
cend

rbegin
crbegin
rend
crend

size
ssize
data
cdata

reserve_hint (C++26)
empty

Range conversions
std::from_range_t std::from_range (C++23)(C++23)
to (C++23)

Dangling iterator handling
dangling
borrowed_iterator_t
borrowed_subrange_t

Range primitives

range_size_trange_difference_trange_value_t
elements_of (C++23)

iterator_tconst_iterator_tsentinel_tconst_sentinel_t

(C++23)(C++23)

range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t

(C++23)

Range concepts

range
borrowed_range
common_range

sized_range
viewable_range
view

input_range
output_range
forward_range

bidirectional_range
random_access_range
contiguous_range

approximately_sized_range (C++26)
constant_range (C++23)

empty_viewviews::empty

single_viewviews::single

basic_istream_viewviews::istream

iota_viewviews::iota

repeat_viewviews::repeat

(C++23)(C++23)

Range adaptors

views::all_tviews::all
as_rvalue_viewviews::as_rvalue (C++23)(C++23)
filter_viewviews::filter
transform_viewviews::transform
take_viewviews::take
take_while_viewviews::take_while
common_viewviews::common
views::counted
to_input_viewviews::to_input (C++26)(C++26)

ref_view
drop_viewviews::drop
drop_while_viewviews::drop_while
lazy_split_viewviews::lazy_split
split_viewviews::split
join_viewviews::join
join_with_viewviews::join_with (C++23)(C++23)
concat_viewviews::concat (C++26)(C++26)
cache_latest_viewviews::cache_latest (C++26)(C++26)

owning_view
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 closure objects
range_adaptor_closure (C++23)

Range adaptor objects

Helper items

copyable-box
movable-box

(until C++23) (C++23)

simple-view
non-propagating-cache

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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)	(since C++20)
template<class R> constexprbool enable_borrowed_range=false;	(2)	(since C++20)

1) The conceptborrowed_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) Theenable_borrowed_range variable template is used to indicate whether arange is aborrowed_range. The primary template is defined asfalse.

[edit]Semantic requirements

LetU bestd::remove_reference_t<T> ifT is an rvalue reference type, andT otherwise. Given a variableu of typeU,T modelsborrowed_range only if the validity of iterators obtained fromu is not tied to the lifetime of that variable.

[edit]Specializations

A program may specializeenable_borrowed_range totrue for cv-unqualifiedprogram-defined types which modelborrowed_range, andfalse for types which do not. Such specializations shall be usable inconstant expression and have typeconstbool.

[edit]Unconditionally borrowed ranges in the standard library

Specializations ofenable_borrowed_range for all specializations of the following standard templates are defined astrue:

[edit]Conditionally borrowed ranges in the standard library

Specialization ofenable_borrowed_range for the following standard range adaptors are defined astrue if and only ifstd::ranges::enable_borrowed_range<V> istrue, whereV is the underlying view type:

(since C++23)

std::ranges::enumerate_view

(since C++23)

std::ranges::take_view

std::ranges::to_input_view

(since C++26)

↑The underlying viewV must also satisfyforward_range.

Specialization ofenable_borrowed_range for the following standard range adaptors are defined astrue if and only if(std::ranges::enable_borrowed_range<Vs>&& ...) istrue, whereVs... are all view types it adapts:

std::ranges::zip_view

(since C++23)

[edit]Example

Demonstrates the specializations ofenable_borrowed_range for program defined types. Such specializations protect against potentially dangling results.

Run this code

#include <algorithm>#include <array>#include <cstddef>#include <iostream>#include <ranges>#include <span>#include <type_traits> template<typename T,std::size_t N>struct MyRange:std::array<T, N>{}; template<typename T,std::size_t N>constexprbool std::ranges::enable_borrowed_range<MyRange<T, N>>=false; template<typename T,std::size_t N>struct MyBorrowedRange:std::span<T, N>{}; template<typename T,std::size_t N>constexprbool std::ranges::enable_borrowed_range<MyBorrowedRange<T, N>>=true; int main(){    static_assert(std::ranges::range<MyRange<int,8>>);    static_assert(std::ranges::borrowed_range<MyRange<int,8>>==false);    static_assert(std::ranges::range<MyBorrowedRange<int,8>>);    static_assert(std::ranges::borrowed_range<MyBorrowedRange<int,8>>==true); auto getMyRangeByValue=[]{return MyRange<int,4>{{1,2,42,3}};};auto dangling_iter= std::ranges::max_element(getMyRangeByValue());    static_assert(std::is_same_v<std::ranges::dangling, decltype(dangling_iter)>);// *dangling_iter; // compilation error (i.e. dangling protection works.) auto my= MyRange<int,4>{{1,2,42,3}};auto valid_iter= std::ranges::max_element(my);std::cout<<*valid_iter<<' ';// OK: 42 auto getMyBorrowedRangeByValue=[]{staticint sa[4]{1,2,42,3};return MyBorrowedRange<int,std::size(sa)>{sa};};auto valid_iter2= std::ranges::max_element(getMyBorrowedRangeByValue());std::cout<<*valid_iter2<<'\n';// OK: 42}