std::ranges::views::elements,std::ranges::elements_view

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

[edit]

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

[edit]

std::ranges::elements_view

Member functions
elements_view::elements_view
elements_view::base
elements_view::begin
elements_view::end
elements_view::size
elements_view::reserve_hint (C++26)
Nested classes
Iterator
elements_view::iterator::iterator
elements_view::iterator::base
elements_view::iterator::operator*
elements_view::iterator::operator[]
elements_view::iterator::operator++ elements_view::iterator::operator++(int) elements_view::iterator::operator-- elements_view::iterator::operator--(int) elements_view::iterator::operator+= elements_view::iterator::operator-=
operator==(elements_view::iterator) operator<(elements_view::iterator) operator>(elements_view::iterator) operator<=(elements_view::iterator) operator>=(elements_view::iterator) operator<=>(elements_view::iterator)
operator+(elements_view::iterator) operator-(elements_view::iterator)
Sentinel
elements_view::sentinel::sentinel
elements_view::sentinel::base
operator==(elements_view::iterator,elements_view::sentinel)
operator-(elements_view::iterator,elements_view::sentinel)

[edit]

Defined in header`<ranges>`
template<ranges::input_range V,std::size_t N> requiresranges::view<V>&& /has-tuple-element/<ranges::range_value_t<V>, N>&& /has-tuple-element/<std::remove_reference_t< ranges::range_reference_t<V>>, N>&& /returnable-element/<ranges::range_reference_t<V>, N> class elements_view :publicranges::view_interface<elements_view<V, N>>;	(1)	(since C++20)
namespace views{ template<std::size_t N> constexpr/* unspecified / elements=/ unspecified */; }	(2)	(since C++20)
Call signature
template<ranges::viewable_range R> requires/* see below */ constexprranges::viewauto elements<N>( R&& r);		(since C++20)
Helper concepts
	(3)
template<class T,std::size_t N> concept/has-tuple-element/= requires(T t){ typenamestd::tuple_size<T>::type; requires N<std::tuple_size_v<T>; typenamestd::tuple_element_t<N, T>; { std::get<N>(t)}->std::convertible_to< conststd::tuple_element_t<N, T>&>; };			(until C++23) (exposition only*)
template<class T,std::size_t N> concept/has-tuple-element/= /tuple-like/<T>&& N<std::tuple_size_v<T>			(since C++23) (exposition only*)
template<class T,std::size_t N> concept returnable-element= std::is_reference_v<T>\|\|std::move_constructible< std::tuple_element_t<N, T>>;		(4)	(exposition only*)

1) Accepts aview of tuple-like values, and issues a view with a value type of theN^th element of the adapted view's value-type.

2) Every specialization ofviews::elements is aRangeAdaptorObject. The expressionviews::elements<M>(e) isexpression-equivalent toelements_view<views::all_t<decltype((e))>, M>{e} for any suitable subexpressione and constant expressionM.

3) Ensures that the elements of the underlying view are tuple-like values, seetuple-like(since C++23).

4) Ensures that dangling references cannot be returned.

elements_view models the conceptsrandom_access_range,bidirectional_range,forward_range,input_range,common_range, andsized_range when the underlying viewV models respective concepts.

[edit]Data members

Member	Description
`Vbase_`	the underlying view (exposition-only member object*)

[edit]Member functions

(constructor)	constructs a`elements_view` (public member function)[edit]
base	returns a copy of the underlying (adapted) view (public member function)[edit]
begin	returns an iterator to the beginning (public member function)[edit]
end	returns an iterator or a sentinel to the end (public member function)[edit]
size	returns the number of elements, provided only if the underlying (adapted) range satisfies`sized_range` (public member function)[edit]
reserve_hint (C++26)	returns the approximate size of the resulting`approximately_sized_range` (public member function)[edit]
Inherited fromstd::ranges::view_interface
empty	returns whether the derived view is empty, provided only if it satisfies`sized_range` or`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
cbegin (C++23)	returns a constant iterator to the beginning of the range (public member function of`std::ranges::view_interface<D>`)[edit]
cend (C++23)	returns a sentinel for the constant iterator of the range (public member function of`std::ranges::view_interface<D>`)[edit]
operator bool	returns whether the derived view is not empty, provided only ifranges::empty is applicable to it (public member function of`std::ranges::view_interface<D>`)[edit]
front	returns the first element in the derived view, provided if it satisfies`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
back	returns the last element in the derived view, provided only if it satisfies`bidirectional_range` and`common_range` (public member function of`std::ranges::view_interface<D>`)[edit]
operator[]	returns the`n`^th element in the derived view, provided only if it satisfies`random_access_range` (public member function of`std::ranges::view_interface<D>`)[edit]

[edit]Nested classes

iterator	the iterator type (exposition-only member class template*)
sentinel	the sentinel type (exposition-only member class template*)

[edit]Helper templates

template<class T,std::size_t N> constexprbool enable_borrowed_range<std::ranges::elements_view<T, N>>= ranges::enable_borrowed_range<T>;		(since C++20)

This specialization ofranges::enable_borrowed_range makeselements_view satisfyborrowed_range when the underlying view satisfies it.

[edit]Example

Run this code

#include <iostream>#include <ranges>#include <string>#include <tuple>#include <vector> int main(){conststd::vector<std::tuple<int,char,std::string>> vt{{1,'A',"α"},{2,'B',"β"},{3,'C',"γ"},{4,'D',"δ"},{5,'E',"ε"},}; for(intconst e: std::views::elements<0>(vt))std::cout<< e<<' ';std::cout<<'\n'; for(charconst e: vt| std::views::elements<1>)std::cout<< e<<' ';std::cout<<'\n'; for(std::stringconst& e: std::views::elements<2>(vt))std::cout<< e<<' ';std::cout<<'\n';}

Output:

1 2 3 4 5A B C D Eα β γ δ ε

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3494	C++20	`elements_view` was never a`borrowed_range`	it is a`borrowed_range` if its underlying view is
LWG 3502	C++20	dangling reference could be obtained from`elements_view`	such usage is forbidden

[edit]See also

ranges::keys_viewviews::keys (C++20)	takes a`view` consisting of pair-like values and produces a`view` of the first elements of each pair (class template)(range adaptor object)[edit]
ranges::values_viewviews::values (C++20)	takes a`view` consisting of pair-like values and produces a`view` of the second elements of each pair (class template)(range adaptor object)[edit]
ranges::zip_viewviews::zip (C++23)	a`view` consisting of tuples of references to corresponding elements of the adapted views (class template)(customization point object)[edit]
ranges::zip_transform_viewviews::zip_transform (C++23)	a`view` consisting of results of application of a transformation function to corresponding elements of the adapted views (class template)(customization point object)[edit]
slice	BLAS-like slice of a valarray: starting index, length, stride (class)[edit]