Namespaces
Variants
Views
Actions

std::ranges::ref_view

From cppreference.com
< cpp‎ | ranges
 
 
Ranges library
Range access
Range conversions
(C++23)

Range primitives



Dangling iterator handling
Range concepts
Views

Range factories
Range adaptors
Range generators
Range adaptor objects
Range adaptor closure objects
Helper items
(until C++23)(C++23)


 
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] Data members

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

[edit] Member functions

constructs a ref_view that references to the given range
(public member function)
(C++20)
returns the references to the referenced range
(public member function)
(C++20)
returns the beginning iterator of the referenced range
(public member function)
(C++20)
returns the sentinel of the referenced range
(public member function)
(C++20)
checks whether the referenced range is empty
(public member function)
(C++20)
returns the size of the referenced sized_range
(public member function)
(C++20)
returns the pointer to the beginning of the referenced contiguous_range
(public member function)
Inherited from std::ranges::view_interface
(C++23)
returns a constant iterator to the beginning of the range.
(public member function of std::ranges::view_interface<D>) [edit]
(C++23)
returns a sentinel for the constant iterator of the range.
(public member function of std::ranges::view_interface<D>) [edit]
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>) [edit]
(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>) [edit]
(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>) [edit]
returns the nth element in the derived view. Provided if it satisfies random_access_range.
(public member function of std::ranges::view_interface<D>) [edit]

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_);.

[edit] Deduction guides

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

[edit] 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.

[edit] Example

#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

[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
P2325R3 C++20 default constructor was provided as view
must be default_initializable
removed along with the requirement

[edit] See also

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