std::ranges::views::enumerate, std::ranges::enumerate_view
From cppreference.com
Defined in header <ranges>
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template< ranges::view V > requires /*range-with-movable-references*/<V> |
(1) | (since C++23) |
namespace views { inline constexpr /* unspecified */ enumerate = /* unspecified */; |
(2) | (since C++23) |
Call signature |
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template< ranges::viewable_range R > requires /* see below */ |
(since C++23) | |
Helper concepts |
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template< class R > concept /*range-with-movable-references*/ = |
(3) | (exposition only*) |
1)
enumerate_view
is a range adaptor that takes a view
and produces a view of tuples. i
th element (the tuple) of the resulting sequence holds:
- the value equal to
i
, which is a zero-based index of the element of underlying sequence, and - the reference to the underlying element.
2) The name
views::enumerate
denotes a RangeAdaptorObject. Given a subexpression e, the expression views::enumerate(e) is expression-equivalent to enumerate_view<views::all_t<decltype((e))>>(e) for any suitable subexpression e.3) 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.
Data members
Member name | Definition |
base_ (private)
|
An iterator to the underlying sequence of type V .(exposition-only member object*) |
Member functions
constructs a enumerate_view (public member function) | |
returns a copy of the underlying (adapted) view (public member function) | |
returns an iterator to the beginning (public member function) | |
returns an iterator or a sentinel to the end (public member function) | |
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range . (public member function) | |
Inherited from std::ranges::view_interface | |
returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range . (public member function of std::ranges::view_interface<D> ) | |
(C++23) |
returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D> ) |
(C++23) |
returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D> ) |
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> ) | |
returns the first element in the derived view. Provided if it satisfies forward_range . (public member function of std::ranges::view_interface<D> ) | |
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> ) | |
returns the n th element in the derived view. Provided if it satisfies random_access_range . (public member function of std::ranges::view_interface<D> ) |
Deduction guides
Nested classes
(C++23) |
the iterator type (exposition-only member class template*) |
(C++23) |
the sentinel type (exposition-only member class template*) |
Helper templates
template< class View > constexpr bool enable_borrowed_range<ranges::enumerate_view<View>> = |
(since C++23) | |
This specialization of ranges::enable_borrowed_range makes enumerate_view
satisfy borrowed_range
when the underlying view satisfies it.
Notes
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_ranges_enumerate |
202302L | (C++23) | std::ranges::enumerate_view
|
Example
Run this code
#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
References
- C++23 standard (ISO/IEC 14882:2024):
- 26.7.23 Enumerate view [range.enumerate]
See also
(C++20) |
a view consisting of a sequence generated by repeatedly incrementing an initial value(class template) (customization point object) |
(C++23) |
a view consisting of tuples of references to corresponding elements of the adapted views(class template) (customization point object) |
takes a view consisting of tuple-like values and a number N and produces a view of Nth element of each tuple(class template) (range adaptor object) |