std::ranges::ref_view

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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)

Atomic operations library (C++11)

Thread support library (C++11)

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<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.

Helper templates

template<class T> inline constexpr bool enable_borrowed_range<ranges::ref_view<T>> = true;

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

Data members

std::ranges::ref_view::r_

R* r_ = nullptr; /* exposition-only */

pointer to the referenced range

Member functions

std::ranges::ref_view::ref_view

constexpr ref_view() noexcept = default;	(1)
template<__NotSameAs<ref_view> T>     requires std::convertible_to<T, R&> && requires { _FUN(std::declval<T>()); } constexpr ref_view(T&& t);	(2)

1) Initializes r_ with nullptr. A default-initialized ref_view references no range.

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

Names __NotSameAs and _FUN are exposition-only. __NotSameAs<T, U> is satisfied if and only if !std::same_as<std::remove_cvref_t<T>, std::remove_cvref_t<U>>. The function _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;

Equivalent to return *r_;

std::ranges::ref_view::begin

constexpr ranges::iterator_t<R> begin() const;

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

std::ranges::ref_view::end

constexpr ranges::sentinel_t<R> end() const;

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

std::ranges::ref_view::empty

constexpr bool empty() const     requires requires { ranges::empty(*r_); };

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

std::ranges::ref_view::size

constexpr auto size() const     requires ranges::sized_range<R> { return ranges::size(*r_); }

std::ranges::ref_view::data

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

Deduction guides

template<class R> ref_view(R&) -> ref_view<R>;

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

See also

reference_wrapper (C++11)	CopyConstructible and CopyAssignable reference wrapper (class template)
views::all_tviews::all	a view that includes all elements of a range (alias template) (range adaptor object)