Difference between revisions of "cpp/ranges/enumerate view"
From cppreference.com
(const on the tuple returned by enumerate is not propagated the underlying reference so additional operation is need to make it const) |
(const qualifier on the tuple returned by enumerate is not propagated to the underlying reference. An additional measure is needed to make it const.) |
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// letter is mutable even with const | // letter is mutable even with const | ||
| − | // to make it const add | + | // to make it const, add {{!}} std::views::as_const |
| − | // or use | + | // or use std::views::enumerate(std::as_const(v)) |
for (auto const [index, letter] : std::views::enumerate(v)) | for (auto const [index, letter] : std::views::enumerate(v)) | ||
std::cout << '(' << index << ':' << letter << ") "; | std::cout << '(' << index << ':' << letter << ") "; | ||
Revision as of 06:47, 30 May 2023
| 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*/ = // exposition only |
(3) | (since C++23) |
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:
- 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.
Contents |
Data members
Typical implementations of enumerate_view hold only one non-static data member:
-
base_of typeV. The name is for exposition only.
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 nth 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 std::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> int main() { constexpr static auto v = { 'A', 'B', 'C', 'D' }; // letter is mutable even with const // to make it const, add | std::views::as_const // or use std::views::enumerate(std::as_const(v)) for (auto const [index, letter] : std::views::enumerate(v)) std::cout << '(' << index << ':' << letter << ") "; std::cout << '\n'; // 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'; }
Output:
(0:A) (1:B) (2:C) (3:D) [0]:A [1]:B [2]:C [3]:D
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) |
