std::ranges::ref_view

 

C++

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)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata 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    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	constant_range (C++23)

Views
view_interface	subrange

Range factories
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 ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while concat_viewviews::concat (C++26)(C++26)	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	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

 

Defined in header <ranges>
template< ranges::range R >     requires std::is_object_v<R> class ref_view     : public ranges::view_interface<ref_view<R>>		(since C++20)

ref_view is a view of the elements of some other range. It wraps a reference to that range.

Data members

Member name	Definition
r_ (private)	A pointer of type R* to the underlying range. (exposition-only member object*)

Member functions

(constructor)	constructs a ref_view that references to the given range (public member function)
base	returns the references to the referenced range (public member function)
begin	returns the beginning iterator of the referenced range (public member function)
end	returns the sentinel of the referenced range (public member function)
empty	checks whether the referenced range is empty (public member function)
size	returns the size of the referenced sized_range (public member function)
data	returns the pointer to the beginning of the referenced contiguous_range (public member function)
Inherited from std::ranges::view_interface
cbegin (C++23)	returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>)
cend (C++23)	returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>)
operator bool	returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
front	returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
back	returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>)
operator[]	returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

std::ranges::ref_view::ref_view

template< /*different-from*/<ref_view> T >     requires std::convertible_to<T, R&> && requires { _FUN(std::declval<T>()); } constexpr ref_view( T&& t );		(since C++20)

Initializes r_ with std::addressof(static_cast<R&>(std::forward<T>(t))).

/*different-from*/<T, U> is satisfied if and only if std::remove_cvref_t<T> and std::remove_cvref_t<U> are not the same type, and overloads of _FUN are declared as void _FUN(R&); void _FUN(R&&) = delete;.

Parameters

t

-

range to reference

std::ranges::ref_view::base

constexpr R& base() const;		(since C++20)

Equivalent to return *r_;.

std::ranges::ref_view::begin

constexpr ranges::iterator_t<R> begin() const;		(since C++20)

Equivalent to return ranges::begin(*r_);.

std::ranges::ref_view::end

constexpr ranges::sentinel_t<R> end() const;		(since C++20)

Equivalent to return ranges::end(*r_);.

std::ranges::ref_view::empty

constexpr bool empty() const     requires requires { ranges::empty(*r_); };		(since C++20)

Equivalent to return ranges::empty(*r_);.

std::ranges::ref_view::size

constexpr auto size() const     requires ranges::sized_range<R>;		(since C++20)

Equivalent to return ranges::size(*r_);.

std::ranges::ref_view::data

constexpr auto data() const     requires ranges::contiguous_range<R>;		(since C++20)

Equivalent to return ranges::data(*r_);.

Deduction guides

template< class R > ref_view( R& ) -> ref_view<R>;		(since C++20)

Helper templates

template< class T > constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true;		(since C++20)

This specialization of std::ranges::enable_borrowed_range makes ref_view satisfy borrowed_range.

Example

Run this code

#include <iostream>
#include <ranges>
 
int main()
{
    const std::string s{"cosmos"};
 
    const std::ranges::take_view tv{s, 3};
    const std::ranges::ref_view rv{tv};
 
    std::cout
        << std::boolalpha
        << "call empty() : " << rv.empty() << '\n'
        << "call size()  : " << rv.size() << '\n'
        << "call begin() : " << *rv.begin() << '\n'
        << "call end()   : " << *(rv.end() - 1) << '\n'
        << "call data()  : " << rv.data() << '\n'
        << "call base()  : " << rv.base().size() << '\n' // ~> tv.size()
        << "range-for    : ";
 
    for (const auto c : rv)
        std::cout << c;
    std::cout << '\n';
}

Output:

call empty() : false
call size()  : 3
call begin() : c
call end()   : s
call data()  : cosmos
call base()  : 3
range-for    : cos

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
P2325R3	C++20	default constructor was provided as view must be default_initializable	removed along with the requirement

See also

reference_wrapper (C++11)	CopyConstructible and CopyAssignable reference wrapper (class template)
ranges::owning_view (C++20)	a view with unique ownership of some range (class template)
views::all_tviews::all (C++20)	a view that includes all elements of a range (alias template) (range adaptor object)