std::ranges::take_view<V>::begin
From cppreference.com
|
constexpr
auto begin(
) requires (
!
/*simple-view*/
<V>
)
;
|
(1) | (since C++20) |
|
constexpr
auto begin(
)
const requires ranges::range
<
const V>
;
|
(2) | (since C++20) |
Returns an iterator to the first element of the take_view.
Overload (1) does not participate in overload resolution if V is a simple view (that is, if V and const V
Parameters
(none)
Return value
The result depends on the concepts satisfied by possibly const-qualified underlying view type Base, which is V for (1) or const V for (2)
Let base_ be the underlying view, count_ be the underlying counter (equals to 0 if take_view
| The underlying view type satisfies ... |
random_access_range
| ||
|---|---|---|---|
| yes | no | ||
sized_range
|
yes | ranges::begin(base_) |
std::counted_iterator
(
ranges::begin
(base_)
ranges::range_difference_t <Base_> (this- >size( ) ) ) |
| no | std::counted_iterator ( ranges::begin (base_), count_) | ||
Example
Run this code
#include <concepts> #include <forward_list> #include <iostream> #include <ranges> #include <string_view> #include <type_traits> using namespace std::literals; int main() { { static constexpr auto v = {"∀x"sv, "∃y"sv, "ε"sv, "δ"sv}; auto view = std::ranges::take_view(v, 8); auto iter = view.begin(); std::cout << *iter << '\n'; static_assert( std::ranges::sized_range<decltype(v)> and std::ranges::random_access_range<decltype(v)> and std::is_same_v<decltype(iter), decltype(std::ranges::begin(v))> ); } { std::forward_list v = {"Ax"sv, "Ey"sv, "p"sv, "q"sv}; auto view = std::ranges::take_view(v, 8); auto iter = view.begin(); std::cout << *iter << '\n'; static_assert( not std::ranges::sized_range<decltype(v)> and not std::ranges::random_access_range<decltype(v)> and std::is_same_v<decltype(iter), std::counted_iterator< std::forward_list<std::string_view>::iterator>> ); } }
Output:
∀x Ax
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2393R1 | C++20 | implicit conversions between signed and unsigned integer-class types might fail | made explicit |
See also
| returns an iterator or a sentinel to the end (public member function) |
|
|
(C++20)
|
iterator adaptor that tracks the distance to the end of the range (class template) |
|
(C++20)
|
compares a sentinel with an iterator returned from take_view::begin (function) |