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.
};|
(C++20) | returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function) |
|
(C++23) | returns a constant iterator to the beginning of the range. (public member function) |
|
(C++23) | returns a sentinel for the constant iterator of the range. (public member function) |
|
(C++20) | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function) |
|
(C++20) | gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (public member function) |
|
(C++20) | 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) |
|
(C++20) | returns the first element in the derived view. Provided if it satisfies forward_range. (public member function) |
|
(C++20) | returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function) |
|
(C++20) | returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function) |
#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
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 |
|
(C++20) | combines an iterator-sentinel pair into a view (class template) |
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