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std::ranges::take_view::begin(3) | C++ Standard Libary | std::ranges::take_view::begin(3) |
NAME¶
std::ranges::take_view::begin - std::ranges::take_view::begin
Synopsis¶
constexpr auto begin() requires (!__SimpleView<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.
1) Returns a std::counted_iterator or a ranges::iterator_t<V>.
2) Returns a std::counted_iterator or a ranges::iterator_t<const
V>.
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 random_access_range
view satisfies
... yes no
std::counted_iterator(ranges::begin(base_),
yes ranges::begin(base_)
sized_range
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 made explicit
integer-class types might fail
See also¶
end returns an iterator or a sentinel to the end
(C++20) (public member function)
counted_iterator iterator adaptor that tracks the distance to the end of the
range
(C++20) (class template)
operator== compares a sentinel with an iterator returned from
take_view::begin
(C++20) (function)
2024.06.10 | http://cppreference.com |