std::ranges::view_interface

 

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

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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

 

std::ranges::view_interface

Member functions

empty

cbegin (C++23)

cend (C++23)

operator bool

data

size

front

back

operator[]

 

Defined in header <ranges>
template< class D >     requires std::is_class_v<D> && std::same_as<D, std::remove_cv_t<D>> class view_interface;		(since C++20)

std::ranges::view_interface is a helper class template for defining a view interface.

view_interface is typically used with CRTP:

class my_view : public std::ranges::view_interface<my_view>
{
public:
    auto begin() const { /*...*/ }
    auto end() const { /*...*/ }
    // empty() is provided if begin() returns a forward iterator
    // and end() returns a sentinel for it.
};

Member functions

empty	returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function)
cbegin (C++23)	returns a constant iterator to the beginning of the range. (public member function)
cend (C++23)	returns a sentinel for the constant iterator of the range. (public member function)
operator bool	returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function)
data	gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (public member function)
size	returns the number of elements in the derived view. Provided if it satisfies forward_range and its sentinel and iterator type satisfy sized_sentinel_for. (public member function)
front	returns the first element in the derived view. Provided if it satisfies forward_range. (public member function)
back	returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function)
operator[]	returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function)

Example

Run this code

#include <iostream>
#include <ranges>
#include <vector>
 
template<class T, class A>
class VectorView : public std::ranges::view_interface<VectorView<T, A>>
{
public:
    VectorView() = default;
 
    VectorView(const std::vector<T, A>& vec) :
        m_begin(vec.cbegin()), m_end(vec.cend())
    {}
 
    auto begin() const { return m_begin; }
 
    auto end() const { return m_end; }
 
private:
    typename std::vector<T, A>::const_iterator m_begin{}, m_end{};
};
 
int main()
{
    std::vector<int> v = {1, 4, 9, 16};
 
    VectorView view_over_v{v};
 
    // We can iterate with begin() and end().
    for (int n : view_over_v)
        std::cout << n << ' ';
    std::cout << '\n';
 
    // We get operator[] for free when inheriting from view_interface
    // since we satisfy the random_access_range concept.
    for (std::ptrdiff_t i = 0; i != view_over_v.size(); ++i)
        std::cout << "v[" << i << "] = " << view_over_v[i] << '\n';
}

Output:

1 4 9 16
v[0] = 1
v[1] = 4
v[2] = 9
v[3] = 16

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 3549	C++20	view_interface was required to be derived from view_base, which sometimes required multiple view_base subobjects in a view	inheritance removed

See also

ranges::subrange (C++20)

combines an iterator-sentinel pair into a view (class template)