Difference between revisions of "cpp/ranges/enumerate view"
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m (fmt) |
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template< ranges::view V > | template< ranges::view V > | ||
requires /*range-with-movable-references*/<V> | requires /*range-with-movable-references*/<V> | ||
| − | class enumerate_view | + | class enumerate_view |
| − | public ranges::view_interface<enumerate_view<V>> | + | : public ranges::view_interface<enumerate_view<V>> |
}} | }} | ||
{{dcl|num=2|since=c++23|1= | {{dcl|num=2|since=c++23|1= | ||
| Line 21: | Line 21: | ||
}} | }} | ||
{{dcl h|Helper concepts}} | {{dcl h|Helper concepts}} | ||
| − | {{dcl|num=3| | + | {{dcl|num=3|notes={{mark expos}}|1= |
template< class R > | template< class R > | ||
| − | concept /*range-with-movable-references*/ = | + | concept /*range-with-movable-references*/ = |
ranges::input_range<R> && | ranges::input_range<R> && | ||
std::move_constructible<ranges::range_reference_t<R>> && | std::move_constructible<ranges::range_reference_t<R>> && | ||
| Line 41: | Line 41: | ||
===Data members=== | ===Data members=== | ||
| − | + | {{dsc begin}} | |
| − | + | {{dsc hitem|Member name|Definition}} | |
| + | {{dsc expos mem obj|base_|private=yes|An iterator to the underlying sequence of type {{tt|V}}.}} | ||
| + | {{dsc end}} | ||
===Member functions=== | ===Member functions=== | ||
| Line 66: | Line 68: | ||
template< class View > | template< class View > | ||
constexpr bool enable_borrowed_range<ranges::enumerate_view<View>> = | constexpr bool enable_borrowed_range<ranges::enumerate_view<View>> = | ||
| − | + | ranges::enable_borrowed_range<View>; | |
}} | }} | ||
| − | This specialization of {{ltt|cpp/ranges/borrowed_range| | + | This specialization of {{ltt|cpp/ranges/borrowed_range|ranges::enable_borrowed_range}} makes {{tt|enumerate_view}} satisfy {{lconcept|borrowed_range}} when the underlying view satisfies it. |
===Notes=== | ===Notes=== | ||
| − | {{feature test macro|__cpp_lib_ranges_enumerate|std=C++23|value=202302L|{{ | + | {{feature test macro|__cpp_lib_ranges_enumerate|std=C++23|value=202302L|{{tt|std::ranges::enumerate_view}}}} |
===Example=== | ===Example=== | ||
| Line 79: | Line 81: | ||
#include <map> | #include <map> | ||
#include <ranges> | #include <ranges> | ||
| + | #include <vector> | ||
int main() | int main() | ||
{ | { | ||
| − | constexpr static auto v = { 'A', 'B', 'C', 'D' }; | + | constexpr static auto v = {'A', 'B', 'C', 'D'}; |
for (auto const [index, letter] : std::views::enumerate(v)) | for (auto const [index, letter] : std::views::enumerate(v)) | ||
| Line 88: | Line 91: | ||
std::cout << '\n'; | std::cout << '\n'; | ||
| + | #if __cpp_lib_ranges_to_container | ||
// create a map using the position of each element as key | // create a map using the position of each element as key | ||
auto m = v {{!}} std::views::enumerate {{!}} std::ranges::to<std::map>(); | auto m = v {{!}} std::views::enumerate {{!}} std::ranges::to<std::map>(); | ||
| Line 93: | Line 97: | ||
for (auto const [key, value] : m) | for (auto const [key, value] : m) | ||
std::cout << '[' << key << "]:" << value << ' '; | 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'; | std::cout << '\n'; | ||
} | } | ||
| + | |p=true | ||
|output= | |output= | ||
(0:A) (1:B) (2:C) (3:D) | (0:A) (1:B) (2:C) (3:D) | ||
[0]:A [1]:B [2]:C [3]:D | [0]:A [1]:B [2]:C [3]:D | ||
| + | 2 4 6 8 | ||
}} | }} | ||
Latest revision as of 11:16, 13 July 2024
| Defined in header <ranges>
|
||
| 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 |
||
| template< ranges::viewable_range R > requires /* see below */ |
(since C++23) | |
| Helper concepts |
||
| 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. 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 |
[edit] Data members
| Member name | Definition |
base_ (private)
|
An iterator to the underlying sequence of type V.(exposition-only member object*) |
[edit] 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>)
| |
[edit] Deduction guides
[edit] Nested classes
| (C++23) |
the iterator type (exposition-only member class template*) |
| (C++23) |
the sentinel type (exposition-only member class template*) |
[edit] 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.
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_ranges_enumerate |
202302L | (C++23) | std::ranges::enumerate_view
|
[edit] 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
[edit] References
- C++23 standard (ISO/IEC 14882:2024):
- 26.7.23 Enumerate view [range.enumerate]
[edit] 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) |
