enumerate_view
is a range adaptor that takes a
view
and produces a view of
tuples.
ith
element (the tuple) of the resulting sequence holds:
i, which is a zero-based index of the element of underlying sequence, and3) Ensures that the reference type of the underlying type can be moved.
enumerate_view models the concepts random_access_range, bidirectional_range, forward_range, input_range, common_range, and sized_range when the underlying view V models respective concepts.
V base_ an iterator to the underlying view
enumerate_view
sized_range
approximately_sized_range
sized_range or forward_range
std::ranges::view_interface<D>) [edit] returns a constant iterator to the beginning of the range
std::ranges::view_interface<D>) [edit] returns a sentinel for the constant iterator of the range
std::ranges::view_interface<D>) [edit] returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
std::ranges::view_interface<D>) [edit] returns the first element in the derived view, provided if it satisfies forward_range
std::ranges::view_interface<D>) [edit] returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range
std::ranges::view_interface<D>) [edit] returns the nth element in the derived view, provided only if it satisfies random_access_range
std::ranges::view_interface<D>) [edit] [edit] Deduction guides [edit] Nested classes the iterator type
This specialization of ranges::enable_borrowed_range makes enumerate_view satisfy borrowed_range when the underlying view satisfies it.
#include <initializer_list>
#include <iostream>
#include <map>
#include <ranges>
#include <vector>
int main()
{
constexpr static auto v = {'A', 'B', 'C', 'D'};
for (auto const [index, letter] : std::views::enumerate(v))
std::cout << '(' << index << ':' << letter << ") ";
std::cout << '\n';
#if __cpp_lib_ranges_to_container
// create a map using the position of each element as key
auto m = v | std::views::enumerate | std::ranges::to<std::map>();
for (auto const [key, value] : m)
std::cout << '[' << key << "]:" << value << ' ';
std::cout << '\n';
#endif
std::vector<int> numbers{1, 3, 5, 7};
// num is mutable even with const, which does not propagate to reference to
// make it const, use `std::views::enumerate(numbers) | std::views::as_const`
// or `std::views::enumerate(std::as_const(numbers))`
for (auto const [index, num] : std::views::enumerate(numbers))
{
++num; // the type is int&
std::cout << numbers[index] << ' ';
}
std::cout << '\n';
}
Possible output:
(0:A) (1:B) (2:C) (3:D) [0]:A [1]:B [2]:C [3]:D 2 4 6 8[edit] References
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