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std::ranges::take_view<V>::begin
|
(1) | (since C++20) |
|
(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
are views with the same iterator and sentinel types).
Parameters
(none)
Return value
The result depends on the concepts satisfied by possibly const-qualified underlying view type Base_
, which is V
(for overload (1)) or const V
(for overload (2)).
Let base_
be the underlying view, count_
be the number passed to the constructor (0
if default initialized).
The underlying view satisfies ... | random_access_range |
||
---|---|---|---|
yes | no | ||
sized_range |
yes | ranges::begin(base_) |
std::counted_iterator(ranges::begin(base_), |
no | std::counted_iterator(ranges::begin(base_), count_) |
Example
#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
(C++20)
|
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) |
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