std::ranges::views::enumerate, std::ranges::enumerate_view - cppreference.com (original) (raw)

std::ranges::enumerate_view

Defined in header
template< ranges::view V > requires /*range-with-movable-references*/<V> class enumerate_view : public ranges::view_interface<enumerate_view<V>> (1) (since C++23)
namespace views { inline constexpr /* unspecified */ enumerate = /* unspecified */; } (2) (since C++23)
Call signature
template< ranges::viewable_range R > requires /* see below */ constexpr /* see below */ enumerate( R&& r ); (since C++23)
Helper concepts
template< class R > concept /*range-with-movable-references*/ = ranges::input_range<R> && std::move_constructible<ranges::range_reference_t<R>> && std::move_constructible<ranges::range_rvalue_reference_t<R>>; (3) (exposition only*)
  1. 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:

  1. 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.

  2. 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.

Contents

[edit] Data members

Member Description
V base_ an iterator to the underlying view(exposition-only member object*)

[edit] Member functions

(constructor) constructs a enumerate_view (public member function) [edit]
base returns a copy of the underlying (adapted) view (public member function) [edit]
begin returns an iterator to the beginning (public member function) [edit]
end returns an iterator or a sentinel to the end (public member function) [edit]
size returns the number of elements, provided only if the underlying (adapted) range satisfies sized_range (public member function) [edit]
reserve_hint(C++26) returns the approximate size of the resulting approximately_sized_range (public member function) [edit]
Inherited from std::ranges::view_interface
empty returns whether the derived view is empty, provided only if it satisfies sized_range or forward_range (public member function of std::ranges::view_interface) [edit]
cbegin(C++23) returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface) [edit]
cend(C++23) returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface) [edit]
operator bool returns whether the derived view is not empty, provided only if ranges::empty is applicable to it (public member function of std::ranges::view_interface) [edit]
front returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface) [edit]
back returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range (public member function of std::ranges::view_interface) [edit]
operator[] returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface) [edit]

[edit] Deduction guides

[edit] Nested classes

| | the iterator type(exposition-only member class template*) | | ------------------------------------------------------------- | | | the sentinel type(exposition-only member class template*) |

[edit] Helper templates

This specialization of ranges::enable_borrowed_range makes enumerate_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_ranges_enumerate 202302L (C++23) std::ranges::enumerate_view

[edit] Example

#include #include #include #include #include   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 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

[edit] See also