std::ranges::ref_view

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

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Filesystem library (C++17)

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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
to (C++23)
Range primitives
range_size_trange_difference_t range_value_t	range_reference_trange_const_reference_trange_rvalue_reference_t   (C++23)	iterator_tconst_iterator_tsentinel_t (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range    sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Factories
empty_viewviews::empty iota_viewviews::iota	single_viewviews::single basic_istream_viewviews::istream	repeat_viewviews::repeat (C++23)(C++23)
Adaptors
ref_view views::all_tviews::all common_viewviews::common owning_view views::counted reverse_viewviews::reverse zip_viewviews::zip (C++23)(C++23) as_const_viewviews::as_const (C++23)(C++23) as_rvalue_viewviews::as_rvalue (C++23)(C++23)	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while zip_transform_viewviews::zip_transform (C++23)(C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)   cartesian_product_viewviews::cartesian_product (C++23)(C++23)	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform adjacent_viewviews::adjacent (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) stride_viewviews::stride (C++23)(C++23)	filter_viewviews::filter join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split join_with_viewviews::join_with (C++23)(C++23) chunk_viewviews::chunk (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23)
Range adaptor objects
Range adaptor closure objects
Helper items
copyable-box	simple-view

 

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

ref_view behaves as if it only stores a R* member subobject pointing to the referenced range. The member is shown as r_ here (the name is exposition-only).

Member functions

(constructor) (C++20)	constructs a ref_view that references to the given range (public member function)
base (C++20)	returns the references to the referenced range (public member function)
begin (C++20)	returns the beginning iterator of the referenced range (public member function)
end (C++20)	returns the sentinel of the referenced range (public member function)
empty (C++20)	checks whether the referenced range is empty (public member function)
size (C++20)	returns the size of the referenced sized_range (public member function)
data (C++20)	returns the pointer to the beginning of the referenced contiguous_range (public member function)
Inherited from std::ranges::view_interface
operator bool (C++20)	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 (C++20)	Returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
back (C++20)	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[] (C++20)	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> { return ranges::size(*r_); }		(since C++20)

std::ranges::ref_view::data

constexpr auto data() const     requires ranges::contiguous_range<R> { return ranges::data(*r_); }		(since C++20)

Deduction guides

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

Helper templates

template<class T> inline 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 <ranges>
#include <iostream>
 
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)