Namespaces
Variants
Views
Actions

std::ranges::ref_view

From cppreference.com
< cpp‎ | ranges
 
 
 
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.

Contents

[edit] 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.

[edit] Data members

std::ranges::ref_view::r_

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

pointer to the referenced range

[edit] 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_); }

[edit] Deduction guides

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

[edit] Example

#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

[edit] See also

CopyConstructible and CopyAssignable reference wrapper
(class template) [edit]
a view that includes all elements of a range
(alias template) (range adaptor object) [edit]