std::ranges::take_view<V>::begin
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Ranges library
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++26)(C++26)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)
std::ranges::take_view
take_view::begin
(C++26)
Member functions
Non-member functions
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 are views with the same iterator and sentinel types).
[edit] Parameters
(none)
[edit] 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 was default initialized).
| 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_) | ||
[edit] 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
[edit] 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 |